I suspect the doctrine for western tanks requires air dominance.

The context here is very specific : Ukraine is attacking a heavily fortified position.

In the beginning of the offensive, the losses were heavy because each time they would break a position with armor, Russians would unleash a barrage of artillery and air bombardments.

Then they changed their tactics, using the tanks as long range heavy direct fire support. And occasionally as spearhead or to counter a Russian offensive.

The biggest problem imo is the lack of air superiority : it makes them vulnerable to air bombardment when on a the front line, and it prevent them from doing deep strikes against artillery.

As they can't prevent artillery or air bombardment, a heavy assault would inevitably suffer extreme losses, but with enough supplies, might be able to break through the line. But the few hundreds of western tanks are not enough for that. Or maybe Ukraine is "simply" afraid of losing too many of them in the offensive.

That's the problem with few, expensive, good weapons: you need to be careful in using them because you can't easily replace them. More numerous, inexpensive weapons would allow to take more risks, which might be necessary to win the war.

I don't know about the US, but France and Germany do had this problem in mind IMO with their light tanks, the amx-30 and the leopard 1.

IMO the heavy tanks are good for an expeditionary force that will be limited in supplies, so it needs to make the most out of each vehicle it gets on the place. But for a large scale war of entrenched position, mass might be more important than raw quality.

More simply, even if you only lose 1 tank for 5 of the enemy, you still need more than a fifth of what they have.

Have you been watching General Dynamics promotional videos?

The early stages of the Ukraine war showed that even massive superiority in combined arms is useless because of how asymmetric warfare has become. Your million dollar tank is just as vulnerable to a $500 drone as a twenty thousand dollar Jeep. Your hundred million dollar jet is still going to get shot out of the air in a CAS role by a $10000 missile. The only wars that the West have been able to fight have been against insurgents riding in the back of old Toyota Hiluxes carrying Soviet-era AK-47s.

Modern Western tank doctrine values crew survivability, even at the cost of maintainability and production capacity. It's the same design principle that the Nazis used to justify the Tiger, Panther, and Konigstiger (mind you, Nazi doctrine also relied heavily on tightly integrated combined arms).