Can only agree - there is no "correct" progression timeline !
Some are natural talents and will evolve rapidly into something way better than the rest of us.
Others just dont have the "thing" it takes - no matter how physical fit they are, and they will stay just above the common "beginner" level
Thats just how things are - and the important thing is, that you are having fun - no matter what level
I would never try to push anyone into something (at least not when you've seen they have a limit) - just help them when they ask for it, or give them polite suggestions, thats the best thing to do IMO
Never try to push - that is YOUR opinion of how it has to be, and not his/hers level
A few people will benefit from being challenged - true - but most dont, especially not if you've tried it and seen a negative outcome, you know it is not the way.
Just my experience from friends and teaching - everyone has fun at their own level