Haven't watched the videos in OP just yet, but definitely interested in them.
But I'll say that having rewatched the whole series with my girlfriend recently, I didn't hate the final season as much as I hated it when it aired.
Part of the problem I had with the final season when it aired was that the pacing was just terrible for a "one episode a week" (with breaks probably) kind of show. The "alternate reality" flashes slowed down any momentum that the main plotline had (the only plotline I was interested in), and even if they weren't there, each weeks episode barely moved things forward. And then there were whole episodes that I felt overexplained things that I feel like could have been better left unexplained (like the entire episode dedicated to Richard's backstory, and the whole episode explaining every part of Jacob and his brother's life).
The alternate reality flashes also ruined all the character's death in the main plotline, because whenever they died there, they just appeared in the alternate reality, so any emotions I'd have felt at any of these character's deaths were robbed, since they weren't "really" dying. Not saying there weren't some emotional scenes with the alternate people getting their memories back and finding their loves, but as I said before, I cared more about the "real" world, not these alternate flashes.
So when the finale rolled around and revealed that those alternate reality flashes didn't have anything to do with the nuke going off last season, and was actually just some kind of purgatory, it made me feel like half the season was not only pointless for the main plot, but also harmful to the story by removing most of the emotional impact of many of the character's deaths in the real world.
But having rewatched the whole season, and knowing about the finale's twist ahead of time, AND being able to binge through multiple episodes in a sitting, the pacing felt less glacial, and knowing the twist meant I didn't have the "are you fucking serious" reaction I initially had when it was revealed. And I did love plenty of the "alternate character's get their memories back and find their true loves" moments.
I still think those purgatory scenes effectively ruined most if not all of the emotional impact of many major character's deaths, and I feel like the last season both explained too many things (I honestly would have preferred not getting a full backstory on Jacob, the smoke monster, and Richard), while also not explaining enough stuff like why the smoke monster leaving would be so bad (he's not all powerful, just get sonic fences and people would be fine), and why saving the island's hole is so important. I guess it could be argued that protecting the island is a matter of faith so you SHOULDN'T know why it has a hole+cork, and the smoke monster is probably a metaphor for Satan or general evil so defeating him is what the characters are SUPPOSE to do because evil is bad.
And I know it would probably have pissed off 10x as many fans as the actual final season did, but in hindsight I'd have loved it if the show at ended with season 5. Juliet just banging away at the bomb and BOOM, cut to white. It would have left a shitload of open threads and would have left the main plotline completely unfinished, but I just loved that season's finale so damn much. If the creators had wanted mysteries left unanswered, that would have been a hell of a way to do it, haha!