Originally Posted by Ironfish653

I’d agree. And it appears to be an older MTB ridden with the seat all the way down and back.
Based on his own description of his pedaling technique, ‘pushing against the seat with the hamstrings’. I’d say the bike is likely to small too.
OP’s pedaling style is what he’s developed to work with a poorly fitted bike.

Cycling, rowing, weightlifting, none of the sports I’ve done that require you to put lots of power through your legs, do you brace against your hamstrings.
To answer the question, if it was a legitimate technique, people would do it.