There really isn't anything :/ In cockpit space combat, decently high skill ceiling, open world with smooth transitions between space and atmospheric fighting. Hard to explain but genuinely nothing exists that comes close. When it works it's really good. There have been periods (usually between patches) where SC was really stable and everything worked quite smoothly.
"When it works" and the time to prepare is the kicker though. Why put yourself through that when you could dive into a plethora of PvP games and actually enjoy your time rather than spend hours setting up or dying to bugs? Games are meant to be fun, not a test of patience.
I mean, yeah, if you really want to limit yourself to cockpit space combat then the choices are slim. But there are "cockpit" based PvP games out there, there are high skill ceiling PvP games out there, all of which you can dive into and actually enjoy immediately.