It depends on how you intemperate that imagery really. To me the flash back wasn't irreverent it just shows how Adachi's perspective was formed and reinforced over time. "The difference between us is that you have a bond" is meant to show exactly that Adachi is very much the antithesis of Yu as you mentioned earlier, and Yu's reply shows that Adachi does in fact have at least one bond despite himself as I mentioned earlier. The power of friendship has always been a part of the story, I don't feel they're whitewashing over the complexity involved with these friendships much either. One of Adachi's lines quite pointedly remarks about how they can't be real friends after seeing each others shadows but we know that's not true. if they do anything wrong it's that they don't delve very deeply to explicitly state how complex these relationships are, the implication is still there though.
Except that's not how the anime choose to interpret it through the actions of Adachi and Yu, not to mention the deliberate use of these flashbacks. The game didn't need the irrelevant flashbacks to Adachi's school life, because it sends a different message then what was originally intended. There doesn't need to be a source, no tragedy, not even an explanation for why humans do what they do, or why Adachi did what he did. Because he already said what he did and there's no larger deeper meaning behind it. Essentially, though, that's what makes him compelling but also dangerous.
The way he phrased it and how Yu seemingly breaks through to him until he arbitrarily turns into Ameno-Sagiri out of nowhere, it implies a different meaning than with the game. It colours him not as a pathetic wretch of a man, but a loner who just needs a hug like your average cliché anime story. They are whitewashing over the complexity by ignoring the central core exchanges between Adachi, Yu and the rest of the cast, and the writing (just like the previous anime) feels lessened and shallow in comparison to the game. The distinct difference is clear though since the anime team isn't the Persona-studio who is making the game, so the adaptation and differences in quality is clear.
Essentially, Yu never really befriends Adachi any more than he does with several of the characters in the game -- He develops a mutual bond of understanding, not friendship, which is where the misinterpration and misunderstading lies.. The general concept of Persona 3 & 4 is to grant a larger understanding of life and death, the reality and inevitability of facing ones own mortality and how death affects the characters individually, and in 4 it's to grasp an understanding of the world without looking back or let yourself be blinded by doubt, shallowness or weaknesses.. I sort of covered that a while back. You build relationships with people to strengthen your Personas, the facets of facing life challenges that we all have, so in that sense you can shallowly argue the "power of friendship"'s integration into the story if you will but I'd hardly argue it a factor. The anime has basically skewered the plot so thin you could spread it on a croissant.