Sure it sounds easy when you put it like that. But then again, you haven't considered everything. So if you have a TH3 army, you count as a TH3? Even if you're a TH11 with infernos and an EAGLE? I can't imagine anything more disastrous for the game or more disastrous for new players just starting out. For that matter, what exactly is a TH11 army anyway? Is a TH11 army the kind of army that someone has the minute their townhall is a TH11 and therefore, new townhalls are considered the same as maxed townhalls? Or is it when they unlock certain troops? Because I know of at least one clan with a monstrously long winning streak who achieved it by doing very much what you described.
How do you score this one offensively?
The solution is far more complicated than you're giving it credit. If it were so easy, it'd be perfect already. The matchmaking still needs improvement for a lot of teams and Supercell will continue to adjust. Keep providing feedback, but let's leave the actual logistics to the professionals. There's a lot more to it than any of us could imagine.