Maybe not as much as Mickey yet, but I do think Mir is still one of the most influential players of all time. The prevalence of 360 tricks and ridiculous zoning (yoyoing in different areas around your body) has largely gone up in recent years after his OWYYC routines. Prior to Mir, people still had zoning in their routines but it was usually only reserved for specific parts of their routines. In recent years, in large part due to Mir, you see routines that feature zoning all the way through with 360 tricks and behind the back tricks and horizontal combos pretty much all the way through.
As for the main question, I would answer it a few different ways.
I do think Mir is the GOAT in terms of technical ability. There are aspects of his yoyoing that aren’t the best, but every player has those shortcomings.
While Mir is still one of the most influential players, in my opinion the most influential 1A players (when talking about competitive yoyoing) have been Mickey, Andrew Bergen, and Takeshi Matsuura. I think a lot of people also say Yuuki Spencer, but that was long before my time lol so I can’t comment on that much.
My personal 1A goat is Ryuichi Nakamura, he’s been competitively relevant for a really long time and is very innovative.