It’s the same man who took 3 years to get some water from Korin, after all. And he was trying dirty tricks to take it, so he wasn’t exactly a fighting genius as Toyotaro portrays him to be
He also never received training from Popo and Kami and so he never learned how to fight with his eyes closed. He also admitted Goku had already surpassed him during Baba’s tournament and in the 22nd Budokai he retired for good after witnessing how the next generation was full of fighters much better and capable than he was. That was his character arc.
Roshi being the first teacher is not an excuse to completely change his character. It shouldn't be Roshi to remind Goku those things, and Goku as the experienced and genius fighter he is shouldn’t be reminded of the basics.
It’s like if Floyd Mayweather’s coach had to remind him how to properly throw a jab and a straight punch, how to guard and to not cross his legs when moving. Basically the most basic boxing things everyone knows. See how much sense it makes?
But suddenly, it turns out that Roshi was an awesome master all the time, but he just refused or forgot to teach his pupils the last and most important training on how to move! It is complete bullshit for Roshi to suddenly have a bootleg version of something as important as Ultra Instinct, when he never showed to have something remotely similar before. What the fuck does it even mean? It’s not UI but follows its “principle” makes no sense whatsoever and is just Toyotaro’s way to justify Roshi having UI but not really having it.
Toyotaro has also tried to sell this technique over power dynamic way too much in a single chapter, out of nowhere. If Roshi could beat Kahseral who is, from his own words, much stronger, then it means Roshi would have been able to defeat Raditz. I don’t know about Nappa, Vegeta or everyone who came later. But Kahseral was basically Raditz in this chapter: a fighter with a higher power level who relies on his scouter to gauge his opponent’s strength, who he deemed completely inferior to his. Too bad Roshi, the real Roshi from the real manga, was scared as fuck when he saw Raditz, and had no balls to go and confront him. Because we know, from basic logic established in the manga, that if Goku and Piccolo couldn’t do shit to Raditz, then neither could Roshi.
The latest Super manga chapter makes no sense to anyone who has read or watched DB by actually paying attention to it. Roshi’s training was all about pure strength, and in fact for Roshi martial arts was all about strength.
Of course he had other teachings but that was the bulk of it. And it was exactly him who taught Goku and the others that martial arts are all about old plain physical strength, definitely not Vegeta or Freeza.
I don’t even care about the dynamics of how Ultra Instinct should or shouldn’t work, and I feel like the posters above me have already done a good job at explaining why Roshi vs Jiren doesn’t make sense in the first place.
What I am more concerned about is that the old man portrayed in this chapter is not the same Roshi from the original manga, and that Goku-looking guy is not Son Goku