The problem is that on top of that Epic has been paying developers extra money to release exclusively on the Epic store (and in some cases it seems they've struck deals for the dev to just not release on steam specifically, but still release on other Epic store competitors). This seems like blatantly anti competitive behaviour to me and I don't want to support it.

If devs were just choosing to not release on steam because epic gives a bigger cut that would be fine, but that isn't the case.