So you're saying that those people that joined 4 years ago joined knowing Corbyn would never lead the UK and they didn't care? As that's where you're basically at. It's not about challenging Corbyn it's about Corbyn realizing that he himself is an impediment to anything he wants to happen ever happening.
No, am sure the opposite is true. many younger people new to politics believed Corbyns popularity would grow bigger and he would sweep to power. older people who had refused to vote Labour joined the party as Corbyn held similar views, it wasn't all about wining a GE, it was also about running the Labour party they way they want it. taking control. they have achieved this so Corbyn is not a failure in their eyes.
Corbyn will not stand down, he has a chance of becoming PM. he has faced harsh criticism all his life, water off a ducks back.
Would a better MP give Labour more of a chance of winning a GE.
Back to my first point, no MP would stand a chance no matter how good they are.
If it came to a head to head debate then Corbyn would be cheered and clapped no matter what he said. the last leadership debates between Smith +Corbyn are still on you tube, have a look if you have time.see who made the best arguments on Brexit etc.