There should be some cap ±~2 levels (or based on team score) so that new players aren’t steamrolled.
In the beginning of the game I was constantly getting raided by players twice my level and it just happened again. It made it extremely frustrating to get my stronghold upgraded when my maxed out mines couldn’t keep up with all the iron being stolen. Now I’m a level 10, getting raided by a 17. Their team scores are not quite double mine but enough that I could never defeat them in my best attempt.
I have a guy on my alliance that got to level 4, never leveled up any of his heroes and just stopped playing. I assume what happened to me also happened to him and he just gave up.