While the creation of a high-power commander who can go infinite with paradox engine the turn it comes out could be a real problem, I think that putting all of the blame on Urza is a bit hyperbolic.
I have seen deck-lists that have or would go infinite (or nearly so) with OG Sisay, Kaho, Selvala 2.0, Jhoira 2.0, Arcum, Emry... the list is bigger than just Urza.
Even if you aren’t running a potential combo as your commander, Paradox Engine is the sort of card that breaks (or enables tremendous leaps in power) if you sneeze on it too hard... and it could be included in any deck as it was colorless. It’s the sort of card that would keep coming up in “Card X goes infinite with Paradox Engine” discussions on a regular basis.
Edit: actually looked up articles from around the time when it is banned. It was said that paradox engine is
“(E)asily inserted into any deck (and) it combines with cards which players already have heavy incentives to play, generating a great deal of mana with virtually no deck building cost.”
Urza probably didn’t help this card but saying that it was banned because of Urza is like saying that Iona died for Kaalia’s sins.