So, there you go.
You asked me if another vilain could beat Sin, and they could.
There's no use trying to deny that fact.
But what should have been written is if another vilain could overpower Sin in versus Combat. Based on Size and force display abilities without the game mechanic of battle of the game.
Then, I'd say no to maybe.
Except for Bahamut who's technically not a villain.
I'd go with Omega Weapon, Or another weapon from FFVII.
As for Machines who could destroy Sin, either SHINRA's military cannon or FFXII's Bahamut. 'oh and by the way, there attacks proved to be one hit kills too'