I agree that ground anti-air has played a larger role in denying either side air supremacy than fighter jets. But it is important to note that Russia failed to establish air supremacy over Ukraine during the almost year before western anti-air arrived. Meanwhile, the Ukrainian air force effectively carried out anti-air missions (including against drones) and even some ground attack sorties.

So, tellingly, the Russian air force failed to establish supremacy over Ukraine when Ukraine fielded only Soviet-era aircraft and anti-air (and in comparatively small numbers). Which strongly suggests that the Russian Air Force is not a particularly good opponent either.

But critically, the Ukrainian Air Force continues to exist as a fleet-in-being. So while it may not currently be capable of much force projection (I would argue that the Russian air force is also not capable of much force projection against a serious adversary), it does force its adversary to strategically deploy anti-air.

As Russian anti-air systems become depleted (which may be sooner or may be later, but due to the rapid destruction of S-400 systems of late, my money is on sooner), it is quite possible that the Ukrainian air force will play a larger role, especially given that training on F-16s commence in a handful of weeks.