I think a lot of what you’re saying is just arguing semantics. There is a very clear and glaring problem with two very conflicting perspectives. Either Leia belives Jedi training would help with dark tendencies, or she believes it would make things worse. What she says in TFA contradicts what Luke says about her here, plain & simple.
I would say that this is just black and white thinking. The life of a Jedi is not easy whatsoever (Qui-Gon line from TPM). There can absolutely be a certain level of fear attached to tackling such a lifestyle without thinking that the whole thing is rigged for you to fail. It’s much more complex than that. On the one hand, Jedi training gives you techniques and exercises to keep your emotions in balance, but it also presents you with WAY more opportunities for things to get out of line - such as being in a lightsaber duel with somebody. We see this all throughout the movie with Rey, where she slips up in highly intense moments. Which is why we may just have to revert to the idea that Leia preferred diplomacy and forming relationships to what the life of a Jedi demanded of her.
And we have TWO whole movies where Leia is very clearly NOT a Jedi in any way. It’s stupid for Rey to suddenly be calling her “master” now (add that to the stupid pile for this movie).
Yes, she didn’t have that role in 7 or 8, but with Luke gone, Rey did need a Jedi teacher to continue her training. Leia very clearly stepped in to fill that role for this film. This is clearly set up at the end of TLJ with Leia being by the broken lightsaber and assuring Rey that they have everything they need. To say that she didn’t become a teacher to Rey is nonsense. You’re the one just arguing semantics by calling her a “mentor”.
Ultimately, while what we’ve got for v5 isn’t perfect (as you’ve demonstrated in some ways), the idea that Leia refused to train over the course of 30 years because of a vision that her son dies on her Jedi path is so unbelievably bad. The first thing Luke would tell her after revealing such a thing is that the last time he made the decision to stop his Jedi training to save his loved ones based on a vision (ESB) it didn’t work out well for him. Nor did it for their father (ROTS). Again, I can understand Luke making a hasty mistake in the hut with Ben Solo, but that’s it.
I think there are ways to improve the dialogue in the scene. Perhaps the first line could be changed to suggest that Leia feared something else, such as temptation. And the next line could say that Rey renewed her faith in both herself and the Jedi. But the throughline on Ahch-To which makes the most sense to me is that everyone has their own fears (everyone is flawed) and that Rey is just as capable as Luke/Leia to overcome them and make the right choices.