Did you ever wonder why Russia has total air superiority over Ukraine? Russia’s anti-aircraft capabilities, intimidating even before the war started, are even greater now after over a 18 months of learning in intense combat. Putting F-16s in small dribbles in the Ukraine theater of war will result of them get shot out of the sky.
Russia does not have “total air superiority”.
It is rather a remarkable circumstance that Russia lacks air superiority. The RuAF is unable to operate over nearly all Ukrainian airspace. This is a consequence of the Ukrainians possessing an effective air defense system. This has kept teh RuAF away for 18 months. This has now been reinforced by western systems, like Patriot.
The Ukrainian AF is also unable to overfly Russian territory, for exactly the same reasons.
Both sides have managed to occasionally operate tactically on the fringes of occupied territories, at the edge of SAM coverage.