Has anybody else noticed that it seems important for the writers behind the Mandalorian and Jon Favreau in particular to stress that Grogu was actually trained significantly by Luke?

Out of universe, Favreau has said multiple times--including recently at SW celebration, that despite how quickly Grogu left Luke in visual media, he actually spent up to 2 years with Luke.

In-universe, we've seen two instances this season of Grogu doing something cool, where Din explicitly makes clear that it comes from Luke's training, not from him. "I didn't teach him that." In one case, it was a force power. In the other it was acting as a peacekeeper and mediator--the core directives of a Jedi you might say.

While I like BTS lore stuff, I tend to avoid BTS politics. That said, the speculation that JF wanted Grogu to have more time with Luke but might have been pressured to rush him back to Din ASAP in the Book of Boba Fett seems frankly reasonable. Who knows?

But in any case, it does seem patent that Favreau wants Grogu and Luke's connection to be significant in terms of Jedi training. Also, in terms of a personal relationship. Two years together would be more of a connection between teacher and student than any other Jedi we've seen after the PT. (Not counting Luke's slaughtered academy students or Kylo).

Personally, I find it kind of gratifying that at least one creative wants to see Luke's legacy as a teacher stand beyond the destruction of his temple in the ST.

Edit: because some people weren't familiar with what he said, a few quotes here:

"We were not on the air for 2 years and we wanted that amount of time to pass in the show."