My basic suggestion is to have equal levels fall in the middle of effectiveness. Say, give jammers a +1 to effective level, so an even ECM vs ECCM shows 80% of normal performance. It's an edge to ECM, but not an overwhelming one. For decoys, instead of capping effectiveness if ECM has an edge, why not let it keep having a bigger edge? Or if that's too much, change the benchmark for full performance from equal levels to a level or two of ECM overmatch. So maybe if you're shooting 5 ECM decoys vs 5 ECCM, each decoy looks like size 3 instead of size 5.
I do generally agree that the ECM/ECCM calculations could use a bit more nuance. I also think how to achieve that nuance is trickier than it seems. One simple change could be to leverage research costs to generate a "pseudo-balance" in ECM vs ECCM at the strategic level.
Yeah, that would work fine. If ECCM is actually about twice as expensive as ECM, then it's reasonable to assume that you'll generally have a 1-level advantage in ECM, and the problem goes away, at least for jammers. I'd still like something else to be done with decoys, because 5 v 5 and 10 v 0 looking the same is kind of absurd.