Even a washed up alcoholic version, knowing that the best version wasn't that good? Let's be realistic here.
It's possibly more realistic to imagine him beating somebody like Sharkey or Gains, than beating somebody like Carnera! Simply a matter of the size differential being more manageable.
Cooney hook was far more deadly than any punch Carnera ever threw, Holmes would have took Carnera out far quicker than Cooney.
I would be more concerned by the lack of ranked contenders on Cooney's resume, and the fact that he was washed up anyway.
The best version of Sharkey probably beats the best version of Carnera. The best version of Carnera should be favored over the best version of Gains. Even if Spinks managed to beat Sharkey, Carnera would probably just smother him.
Yeah a 200+ pound Spinks would do very well in that era. He'd likely have even given Joe Louis a competitive and memorable fight.