A combination of 1 & 3 seems highly likely in my uninformed opinion. Economically, losing aircraft will make a war very expensive very quickly. Losing large numbers of top of the line aircraft will severely harm Russian military aircraft exports.

With Europe closing its airspace there aren't many valid approach paths into Ukraine, or ways to get out of Ukraine should things go south. Russia has few stealth aircraft. In the 1991 gulf war, 60's era Soviet SA-2 missiles were able to defend Baghdad against non-stealth aircraft despite weeks of Suppression of Enemy Air Defenses(SEAD) strikes.

A MIG-29 costs ~20 million dollars new.

https://en.wikipedia.org/wiki/Package_Q_Strike

>With Europe closing its airspace there aren't many valid approach paths into Ukraine

Europe only contacts the western border. Russian aircraft can approach from the north (Russia and Belarus), south (Black Sea) and east (Russia).

I've often suspected that the F-35 was so expensive only a handful could be built, and would not be risked in combat because it was too expensive to replace.

The F-35 isn't that expensive these days. It's still a huge amount of money to spend on something good for nothing but war, insert your view here, but the price isn't much different than the new F-16s being bought by the Israelis.

That being said however stealth aircraft are not cheap to maintain at all.

Curiously I wonder if a similar problem is occurring with SA-400 missiles and other Russian air defenses. They may be too expensive to shoot at low cost drones such as the bayaktar.

I can imagine a considerable problem with the command structure is that if you've got a war that forces are badly prepared for and reluctant to fight in, you have to tread much more carefully with the orders you give your small number of highly trained (and relatively smart) pilots based on home soil than your large number of dispensible conscript troops you've driven into the conflict (or your gung ho special forces). Easier for them to disobey, and much more cause for alarm if they do, and no matter how dedicated they are to following orders, there are fewer pilots and planes to risk than armoured personnel carriers, artillery units and dated tanks.

> it suggests severe problems with their command structure

This is what my money is on.

Sending ground forces in without establishing air superiority is ludicrous, for reasons that we are seeing now. I guess we have a good idea where the military coup will originate.