The winner of a "free for all" is not always the strongest participant.
You people do realize that in any "free for all" the combatants form temporary truces to take out the #1. In this case it'd be Hashirama.
If you step back and take a clean look at it, Tobirama, Hiruzen, Minato, and Tsunade wouldn't be stupid enough to worry about each other when Hashirama is on the field looking for blood. They'd gang on up him to take him out of the picture and then get on with it. Unless Hashirama is strong enough to take out the combined force of Tobirama, Hiruzen in his prime, Minato, and Tsunade, then he won't win.
Okay what if the 4th hokage had Sage mode... Cause I'd assume if he did reach his prime he'd only mastered sage mode and prob. have another variation of fgt.
It's doubtful that Minato had Sage Mode. It's doubtful that he'd have been qualified to even learn Sage Mode.
Fukasaku told Naruto that only those with extremely large chakra reserves (like Jiraiya and Naruto) have the chakra that it takes to balance the massive influx of natural energy. Unless there's ever been any reference to Minato having such large chakra reserves, it's meaningless to talk about Minato and Sage Mode
Only a select few are capable of learning SM.