You can't argue that Grogu is too young and dumb to focus on his training and also miss Mando while simultaneously saying that he's mature enough to make a massive life choice like "do you want to be a Jedi or do you want to be a bounty hunter's sidekick". Yeed is a child. There is no urgency to his training, and it's not like he wouldn't naturally get over his attachment to Mando with time. The obvious solution would be to just to tell Mando "sorry this is a crucial time in Yeed's development and he can't deal with you distracting him so please stay away for a few years" while they continue to train him.
But that can't happen because this false dilemma is necessary for the future of the franchise. Yeed is bankable and Disney doesn't want to give him up, but they also don't want to have to have CGI Luke feature prominently in the story. So the solution is to write Yeed out of the training with Luke.
And that's fine. I don't particularly mind it, but let's not pretend that Luke forcing a toddler to make a major life decision like this is good writing.