Considering that legends Luke is considered to be the best duelist in history and combined 3 forms into his own hybrid form, my answer is yes without question

^Right. He trained multiple generations of Jedi in his NJO so this is a very easy decision for me too.

I probably know the answer to this, but I’m curious: Do you think Legends Luke ever mastered Form III to the same degree as Obi-Wan Kenobi?

Form III is one of the forms Luke has in his hybrid form. So yes. Luke’s form had traces of Form III, Form IV and Form V mixed together with his own techniques.

Imo maybe. Form lll was Obi Wan’s go to fighting style in nearly every fight he participated in while Luke, as Scott pointed out, mixed a variety of other forms to go along with Form lll. As he got older he definitely took a more defensive approach to his fighting.