Think I know where you are coming from Crackle and this is something I can sympathise with being 6'2" and fairly hefty. I think your basic premise is correct, providing you have good cardio-vascular fitness (which is exactly what you get from cycling) then carrying a few extra kilos doesn't matter so much healthwise. However I think there are practical and long-term difficulties maintaining this.
Firstly you're very lucky if you can consistently stay "a few kilos" over as you get older, it does tend to sneak up on you, especially if, like me you carry the weight fairly evenly and don't have a particularly fat gut or arse, you just tend not to notice gain too much. Secondly you may be fit and physically strong but it doesn't necessarily follow your skeleton is any stronger. I'm a keen skiier and I notice every extra kilo on my knees.
I'm also a mountain biker and it is pretty difficult setting-up a bike over about 95kg, even if you change to heavyweight springs, you just can't dial-in the suspension of nearly every bike I've tried. It also helps if you don't fall like a sack of spuds. Similarly on road bikes, you need to put 23c tyres way beyond their rated pressures to work properly. The chart recommending pressures on a michelin pro-race indicates the maximum pressure corresponding to an 85kg rider!! I have them up at 140-150psi...
So like most things, not black and white, especially if you want to stay active as you age.