TLJ has a few unnecessary jokes but I don’t think that’s sufficient to claim it’s trying to be a Star Wars parody. It’s sincere enough when it needs to be - Kylo asking Rey to join him; Luke and Leia’s final scene; Luke’s death etc. In many ways moments like the BB-8 coin gag and the porg jokes feel like The Phantom Menace-style (or Special Edition Mos Eisley-style) humour to me, which I also don’t particularly enjoy in those movies, but is certainly a part of the franchise’s identity at this point. It’s also fairly straightforward to trim out, and I confess I am somewhat more sympathetic to movies which lend themselves to being easily tweaked via fanedit.
Yes, Luke on the island is not acting as the rebel we remember him as. This is because of his emotional trauma. The movie spends a lot of time on this, and I suppose if you just don’t buy in to it, you just don’t buy in to it. While TFA does say he went to the first Jedi Temple, it also very explicitly lays out that he “walked away from it all” - had TLJ failed to acknowledge or develop that, it certainly would have been guilty of ignoring TFA’s plot threads.
Having to deal with two sets of main characters, the new and the old, is one of the burdens the sequel trilogy always had to bear by virtue of being sequels to the OT - it would’ve been a shame if Luke hadn’t gotten some substantial chunk of screen time. I feel TLJ does a good job of finding a way for our new protagonist and our old protagonist to share a lot of that screen time and move each other’s arcs forward to make the most of it (and the force bond to allow Rey to also interact with Kylo is an excellent trick). Rey still gets plenty of development, and takes meaningful action to move the story forward when she decides to go try to turn Kylo, when she rejects his offer, and when she saves the Resistance. And Rey isn’t still in search of a father figure at the end of TLJ - like Leia says to her: “we have everything we need”.
Leaving so much of Ben’s backstory to out-of-movie material is admittedly one of the weaker aspects of the sequel trilogy IMO, since the audience is supposed to sympathise with his redemption in TROS. TFA alludes to it with the conversation between Han and Leia (“I just never should have sent him away.”) but we don’t get much of Ben’s perspective on his childhood or his life prior to collapsing the hut on Luke. Then again, the same is true of Vader in the OT - the audience didn’t have the full picture of why he turned to the dark side until ~20 years after ROTJ came out, right? He never even mentions Padme in the OT, and instead seems to wax on mostly about how much he loves “the power of the dark side”. Kylo Ren will never get his own prequel trilogy, but The Rise of Kylo Ren comic, the Age of Resistance: Kylo Ren comic, and bits and pieces in Aftermath, Last Shot and Bloodline sketch out the broad strokes. He is supposed to seem, to some extent, like a victim of Snoke’s manipulations, someone who’s currently on a bad path but isn’t fundamentally evil - but a lot of this is just conveyed in the movies by Adam Driver’s performance rather than anything explicit so I can see why some do write him off as a “mentally-ill punk”.
Yes, the TLJ marketing capitalised on the shock value of “it’s time for the Jedi to end”, and then in the movie itself Luke starts out espousing that rhetoric but stops doing so by the end of the movie. This is just the plot of Luke’s arc, right? Like how ROTJ’s marketing plays with the idea Luke might turn to the dark side, and then he doesn’t. It’s the story. The movie itself isn’t trying to convey to the audience that the Jedi actually need to end. That’s just what Luke tells himself to justify his exile. And once he emotionally tackles the real underlying reasons for that exile, he stops with the lie he has been telling himself, too. If anything, the intended “message” of the movie is the one delivered by Yoda, that we should learn from what’s good about the past (our “masters”) while seeking to progress beyond it. No point throwing the baby out with the bathwater.
I disagree firmly with any ideas about grey Jedi, or using both the light side and the dark side, because Lucas was pretty explicit in the point that the dark side is inherently corrupting and a very slippery slope. Its whole purpose in the wider allegory of Star Wars is to represent difficult to escape cycles of negativity, like drug addiction, abuse, violence etc. It’s the temptation to do bad and selfish things. Lucas is a big proponent of people acting selflessly, since he believes that’s the way to real happiness. It’s a straightforward moral message, but that keeps it easy for kids to understand. While it’s tempting to see using the light side and dark side as some kind of integrating the shadow, best of both worlds, enlightened centrism thing, that’s not what Lucas meant by balance, because it just inevitably leads to more and more dark side usage. The dark side is the imbalance: if you start down the dark path, forever will it dominate your destiny. That crack is really moreish.