Why would the last Jedi Master go looking for the history of the Jedi Order? Why would he also go into hiding after he failed as a Master and his Padawan became the next Darth Vader? Those seem like two pretty compelling reasons. He went to find a place to die because he couldn't handle that he nearly murdered his nephew in his sleep, and that nephew destroyed the new Jedi Order. Then the nephew became a bigger threat to galactic peace than Vader was (if you go by "number of planets blown up.")
They were trying to keep Luke's deal a secret in TFA. Nobody had seen him in years, and the whole movie revolved around the map. Han says that Luke went looking for temples. It's left to the viewer to piece together that the map left by Luke would lead to the temples and not the man himself. A map to an individual person, who's got a spaceship is just a silly thing. But it's simpler to say "it's a map to Luke" than "it's a map to a possible location for an ancient Jedi Temple. Maybe even the first Jedi Temple. If Luke completed his quest to find the first Jedi Temple, this is where he'd be." It's not spoon-fed to you, but it doesn't take a huge leap to understand it.
You've got it exactly right that TLJ tried to do its own thing. I've said that it's Rian's personal speed bump in JJ Abrams' sequel trilogy, which forced JJ to squeeze two movies into the Rise of Skywalker.
Speaking of Luke's spaceship: How did he get to Ahch-To? He didn't have an astromech droid. Unless he sunk the droid with his ship or dismantled it.
the problem with this narrative is this depicts 2 different characters. The last Jedi Master going to seek more knowledge in the Jedi temples makes sense. However, this implies he seeks further knowledge because he wants to redeem his mistake which is raising Kylo Ren. It could be finding a way to bring him back to the light, searching for new insight, etc. The point is these are not the actions of a man who is suicidal or looking to die.
You are also mixing up the narrative between TFA and TLJ. It’s not revealed that Luke attempted to kill his nephew in his sleep, that he is looking to die, or that he thinks the Jedi should end until TLJ. TFA is a mystery of where did Luke go and what is he doing despite the galaxy being in peril.
That’s why it feels like a 180 when Luke throws the saber away and is just living and roaming as a hermit In TLJ. This is a guy who dove head first to confront Vader when he wasn’t ready to save his friends but here he is trolling Rey despite even more wanton death. The striking Ben in his sleep is also a reverse of his development in RotJ and is a slap to the fans.
I would say TLJ is more than a speed bump. TLJ cut every single narrative plot line Abrams had set in TFA with nothing to work with.
1) Luke - dead and a non factor.
2) Snoke - dead and a non factor.
3) Rey backstory - she is a nobody.
4) kylo v Rey - it’s 0 - 2 for Rey and she isn’t losing in the final battle.
the finale of TLJ was setup as the resistance vs the First order with Kylo in charge with the final conflict being Kylo vs Rey with Rey winning.
