So the subjective part is the question of is he one of the best of all time. Sure, we can have that conversation. But the part where you’re outright wrong is where you exclude him from being remotely close to that conversation.
As a guitarist, Prince has:

• Impeccable musical ear
• Intuitive note selection
• Technical mastery of the instrument
• Perfect timing
• Improvisation so good you couldn’t sit and write better lines
• Riffs for days
• Sold 150000000+ records, in a time when that mattered

I think the above definitely puts him in the running. You might not like it, but he’s up there. I’d rather collaborate with Prince than Eric Clapton, say, and he’s supposed to be one of the greats. I think Knopfler breasts Prince quite handily, but I’m not so sure George Harrison was better. (I’m sure George would say Prince was better)