Can someone explain to me how is Tony Stark a good mentor?

He is an aspiring mentor. 😏

As I see it, him mentoring Peter is something he’s supposed to struggle with. Tony wants to do the right thing and give Peter good advice, but ultimately finds it difficult because he ends up being a father figure (a very inexperienced one) who wishes to make up for what he didn’t have. Moreover he does realize he’s not the best person to be mentoring a kid (hence him telling Peter “don’t do anything I would” & “I wanted you to be better”), and that becomes even clearer to him after the Ferry incident. Nevertheless, he knows he took an important role and genuinely wants what’s best for Pete.

I think this all makes the Peter-Tony dynamic more interesting.

They wanted it to be similar to the Ultimate comics where Peter has a protector/friend but instead of using Nick Fury (who hasn't as much relevance since Shield was gotten rid of) they went with Tony Stark.

He's not. He yells at Peter for trying to fight the Vulture and takes his suit. Then, Peter does the exact same thing (only this time he doesn't cause collateral damage) and Tony is like, "Good job, kid! Here's your suit back! Way to fight the Vulture even though I took your suit in the first place because you fought the Vulture."