I'm sure that the bike is heavier, but the tires and front suspension probably had more to do with your experience than the weight. Had your son's bike been a mid-range road bike of the same era, you would have been fine. You probably would have been pretty OK with a locked-out suspension and slick tires, too. Even better if the bike were in tune.
Apples to oranges, I think.
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The bicycle, the bicycle surely, should always be the vehicle of novelists and poets. Christopher Morley