I saw this topic earlier this week and I thought of what post to make but nothing came to mind. It's a kind of hard because I am not a game developer as I do not actually play games due to the stress load of things on here.
So far, most of the games I have played are somewhat easy to play. If I am to make a game, I will make an arcade game,where the side characters don't stand at a place to be killed by the main players. If i am to build a game, I would want to build a game where the side characters get to learn from the mistakes that got them killed, making them upgrade in battle experience and know how to counter a previous mistake.
This will continuously improve the difficulty of the game and at the same time, improve the main player. To make it more interesting and less frustrating, the ratio by which the side players learn from their mistakes will be somewhat slower than the speed inwhich the main players learn.
I think this feature will help players not underestimate any game and feel good when they are playing any game.