Were Heavyweights in past generations small/lighter due to the 15 rounds?

[ShoulderRoll]

I'd back Fury to last 20 rounds, never mind 15. Nash out.

He's gotten too fat to go 15 rounds effectively.

[QueensburyRules]

Yes.

Both Fury and Wilder were huffing and puffing in their last fight. Anthony Joshua looked gassed against little Usyk. These big guys aren't built for 15-round-wars.

- - Can't imagine U teensy heavies going that far against today's big boys.