Looking at the Russo-Ukrainian war, battery-powered drones seem to be more important than tanks right now. Russia, famously, had a lot of tanks; now, Oryx has a lot of their metal carcasses. Gone are the days of mass T-34 attacks that decided entire wars.
I will concede your point on heavier aircraft, though.
Between zero fossil and full fossil there's a world of nuances, too often ignored. How much oil are those heavier aircraft using, as percentage of the whole country usage? The difference is the answer needed.
It is not just oil, but the necessity to keep up the entire separate infrastructure for its refining, processing, storage and distribution.
Imagine a world where the railroad, for some reason, is still stuck with steam engines and black coal. Everything else moved on, but they cannot, thus keeping the mines open etc. Very uncomfortable and far from optimal.
We still have coal mines open, what do you mean? For less and less uses, yes, but they still have their uses, and we are not (nor should be) judging them for that.
The last coal mine in my country just closed a few days ago, 244 years after mining started. I am a bit influenced by this, because I live in that region.
Everyone with any military training has been laughing at how bad Russia was using their tanks, thus allowing them to be destroyed. Losing some tanks in battle is a given, but it is generally believed that if Russia was using tanks according to the Soviet doctrine they knew well they would not have lost near as many - as proof of that Thesis, Ukraine has been using the Soviet doctrine and not lost nearly as many tanks. (Ukraine lacks enough artillery to apply the Soviet doctrine of war which is why they are using drones - they have now developed new styles of fighting that uses the drones they have, but tanks are still an important part of war)
Tanks are the heavy cavalry of the modern era, their main use is to break defensive lines.
Or rather, was. Neither the Russians nor the Ukrainians, operating diverse tanks on the bases of different doctrines, managed to do much breaking with them. The battlefield of today is just too different and much more hostile to anything that moves in the open and is big and slow enough to get hit.
I will concede your point on heavier aircraft, though.