Firstly, i doubt it’s got anything to do with you being being shorter than them, so don’t use that as an excuse, yes they’ve got the extra leverage but they’ve also got to put in the extra effort to keep those levers turning.
Ideally as most roadies will tell you(i’m not one)a fast cadnce is important and more efficient, but if spinning them like that hurts try digging in deep and grind out a bigger gear at lower cadence.
I’m sure there’s alot more knowledgable riders out there than me, on thursday i did a 90miler over 5 hrs and still had short sprinting power at the end of it and no aches at all.
You could try riding with a different slower group to make you feel better ..most of this is in your mind and not feeling the pain will build your confidence, yes it will hurt, effort is meant to, to a degree..
Your problem is you’re feeling the pain through anticipation of it hurting, how many times do you for instance do something and react as if it hurt, where it didn’t really hurt at all, ie, stub toe, bash leg, etc……
And now seeing how much you normally ride, i’d say you may need to recover abit more between rides and do some stretching..perhaps, dunno i just wing riding bicickles..