Some people seem to prefer late (i.e. dead) teachers. Maybe the reason is that, frozen in time, their thoughts can now be considered ‘definitive’ and appropriated as ‘truths'… To deal with a live teacher, one can only see their thoughts as topics of enquiry, of search… but that means hard work.
Clinging to certainties is so much more reassuring and so much less work! It's great for internet memes, too: a cheap way to appear wise by association.

Some people seem to prefer dead teachers. Maybe the reason is that dead people don't need shelter, food, clothes and medicine. One can share Alan Watts’ or Krishnamurti’s material indefinitely, without ever having to offer them a meal.

Some people seem to prefer books or even videos. Maybe the reason is that such materials freeze a teacher's thought at a particular point in time. The reader can then relate to who the teacher was (when his/her thoughts were recorded) and ignore the hard work that “exploring together” would entail. It often is a convenient way to prematurely kill the teacher.
And if a teacher shakes things up a bit too much for it to be comfortable, to relate to him/her via books is so convenient for the ego: one can then simply “turn the page” and find another teacher to read (but not to connect too deeply with).

The clarity on pariyatti, paṭipatti and paṭivedha comes mostly from the commentarial literature, even if the Buddha himself somehow explained each approach separately (e.g. in the Sallekha Sutta, MN 8, where he concludes that the task of a compassionate teacher is the correct exposition of his/her teaching, while that of a disciple is the practice, paṭipatti). In general, we can use theory, practice and insight for equivalence.

Learning the theory of violin playing might allow one to better appreciate the performance of violinists, and might even be useful to rank performers.
In relation to a spiritual teacher, ‘knowing’ some Dharma might allow to assess whether a prospective teacher is consistent with the Buddha… or is making things up (e.g. blabbing about ‘karma’ but then making it deterministic or limiting it to our human experience here on this Earth).

Practicing violin playing might also allow one to better appreciate the performance of violinists, and might even be useful to rank performers… Yet this is done at a completely different degree.
One might for example understand why a performer deviated from the composition, based on the context at hand (from personal constraints —e.g. an injury preventing a particular gesture— to environmental constraints —e.g. other musicians rushing), no longer clinging to the fallacy that “agreement with theory” is the perfect yardstick.
In relation to a spiritual teacher, one's ‘practice’ of the Dharma might allow to relinquish unrealistic expectations about teachers, to relinquish myths about the existence of ‘perfect’. Generosity finds practical manifestations, Compassion too… Studying at this level allows the practitioner to consider the ‘Perfected’ Qualities (paramita) beyond their caricatures, and to truly cultivate them, without falling into impatience, judgements of inadequacy, or despair.
At the level of ‘practice’, one might let go of the fetter of rituals, fixated forms, and reconnect with one's creativity, to find how to manifest the teachings without a form being predetermined.

The last degree is more subtle, yet most people can understand that a violinist never reaches a point at which ‘practice’ becomes unnecessary: not only the performer evolves (physically, technically, mentally…) and has to learn how to respond in violinistic terms to such an evolution, but also most skills are perishable. Moreover, even for skills that would not be perishable, the very idea of acquiring the skills lies in the value created when later using the skills!
In relation to a spiritual teacher, insights in the Dharma might allow not only some autonomy from teachers, but also some understanding that autonomy doesn't negate the value of dialogue: the relationship teacher-student evolves, becomes more equal, it might become collaborative, but it doesn't necessarily cease… ‘Insights’ make one realise that a teacher is not a requirement to see reality as it is, and yet the teacher plays his/her part within that reality: one finally sees how one is neither dependent nor independent, so realising ‘selflessness’ finally becomes an actual possibility! And one can remain a ‘student’ while helping others and becoming a ‘teacher’ oneself (it's a false dichotomy to think that, because one is ‘teaching’, one no longer needs to learn).

The trends of spiritual materialism (accumulating merits but also teachers ‘followed’, books ‘read’ and videos ‘seen'…) and of consumerist individualism (“I know best what I want and I'm entitled / I have a right to chase what I want”) endanger the spiritual search of many.

This is often manifested by idealising late teachers (and their teachings frozen in history) and by focusing on doctrines: such behaviours just make it easy to grasp, or drop, views based on personal convenience at any given time. Unfortunately, “I only do what I want to do”, “I only read what I want to read”, “I flip-flop whenever I want”, or “I stop whenever I find things uncomfortable” do limit one's practice to the first stage only: theoretical knowledge.
By construction, egotistical ignorance will always reject what might actually challenge it. Ignorance perpetually raises barriers and veils, to prevent insights… and its best strategy is often to find excuses not to even embody the ‘practice’ (too hard, no time, no resource, etc.)!

Trust should not be given blindly to any ‘teacher’ (cf. finding a ‘good’ teacher), and yet, without trust in some Dharma friends, barriers are unlikely to be shattered, breakthroughs are unlikely to happen, samsaric perpetuation wins: “I know better” almost invariably leads to “oops, I bumped once again in the same mistake (because, when someone tries to help me in advance, by warning me of the unhelpful consequence coming, I refuse to consider I might be wrong, that's too uncomfortable to contemplate)“.

The Buddha referred to the Dharma with the parable of the ‘raft’: after crossing the river with a raft, you don't need to carry the raft with you, it has played its function, no need to cling to the solution to an old challenge in front of new challenges… But abandoning the raft prematurely might be unsafe: acting as if you already reaped the fruits of seeds you didn't yet sow is unwise. Not building the raft at all, on the basis that its use will not be permanent, might perpetually prevent the crossing.
Similarly, clinging to a teacher after crossing is inappropriate: instead, you look at the next challenge and act appropriately (maybe it involves collaborating with your teacher to help others, but that's out of taking responsibility to wisely help others, not out of clinging to a “my teacher/school is the best” fallacy). However, pretending you can dispense from having a teacher you trust, prior to the crossing, on the basis that you will not need one after the crossing, might perpetually prevent the crossing…

Be bold, embody practice! Find yourself a teacher (or two…), alive, that you're ready to follow even when their instruction might push your limits. Finding such a guide might be hard, it may take times, it might iterate with trials-and-errors, it may require learning about one's own biases along the way (cf. projections on teachers: links + video), and yet, without guidance to challenge our habits and views, we all tend to go round in circles.

calmly helping to stop the delusions of "having figured it out"

Cherry-picking books and videos that you agree with will not cut through defilements, will not challenge prejudices! Contradiction with views is necessary for insights. Past teachings do often provide the necessary material (cf. All these sūtras contradict one another!) but cherry-picking commonly gets in the way!
A dead (or at least absent) teacher cannot point out to you your cherry-picking.
Nor can (s)he calmly help you stop your hyper-activity or your delusions of “having figured it out”…
It doesn't need to be formal, but it needs trust (so that you can listen and become acquainted with another perspective than yours). Trust is not magical: it's the consequence of an assessment.