That was a very long winded way of saying "not actually just multiplying everything together"
Given the new two-step system, you still have a problem with counters.
Given a 90% ECM, there is no way to counteract its effects with a superior sensor.
Consider troops and spotting. What is the benefit of camo gear? Quite a lot. If you add a thermal sensor, it should bring the chance to spot back up to better than before the camo gear came out. But it can't under your given system since that defense avoid% is guaranteed. (You'd have to add a complex web of interdependencies to each factor)
The way I'd do it is have a base attack value of 50, and a base defense value of 50 (say, settings.txt)
50/(50+50) = 50% to hit
Camo gear = 150pts defense.
50/(50+200) = 20% to hit
Thermal scanners = 250pts attack.
300/(300+200) = 60% to hit (vs camo, or 86% vs normal).