Fury's size might not help much against Usyk.

Except Fury was not 21 years of age. Your point would hold merit if Fury was only 2 years into his own boxing career at age 21, starting his career at age 19, and fought Wladimir Klitschko at age 39 whilst Wlad was 2 years away from retirement. If that was the case, then I'd grant you it'd be a much more of a level playing-field because one guy would be only 2 years into his pro career (Fury) whilst the other guy would be 2 years away from retirement (Wladimir Klitschko). Only problem is, Fury was 8 years into his pro boxing career when he faced Wladimir Klitschko and has fought on for another 5 years after fighting Wladimir Klitschko whereas Wlad was 2 years away from retirement and had 19 years of mileage as a boxer (including training camp for a guy who is 6 foot 6, 240 pounds) when he faced Fury. The example you provided, is not even remotely comparable to what happened in reality.

Once again, there are significantly more cases of a 27 year old heavyweight at the top level, dethroning a 39+ year old champion WAY past his prime than vice versa. To say this rule doesn't apply to Wladimir Klitschko, even though it applied to pretty much every past heavyweight, is what's known as 'SPECIAL PLEADING'. Your justification for why this rule doesn't apply to Wlad (because Wlad is a super heavyweight or he's too modern and blah blah blah) are just unproven assertions, which you need to substantiate. Until then, your position falls apart.

 

Fury batters and knocks out the hyped Usyk. It will be a complete mismatch.