Who would be the G.O.A.T if fights were only 4 rounds long?

For 1 or 2 rounds it would be Tor Hamer.

 

Foreman was still eating most of the clean shots in the first 4 rounds against Ali. Forget all the revisionist history about the rope-a-dope, and how he was winning by a lot until he tired.

Ali was landing clean shots to Foreman's head all night.

 

Possibly De La Hoya, I seem to recall it being said by someone that he was the best 8 round fighter ever. Cut it down to 4 and there you may have it

 

Fighters would fight differently, so it's impossible to judge.

Just like how people say if Leonard-Hearns 1/Marciano-Walcott 1/Louis-Conn 1/Weaver-Dokes were scheduled for 12, the results would have been different.

Well they would react differently to different situations so it's impossible to tell.