Supersonic speeds would certainly be used for beyond visual range (BVR) engagements. Higher speeds mean you and your missiles have more energy and maneuverability. Since the F-35 needs to use it's afterburners to reach supersonic speeds, it likely wouldn't use the extra fuel just for transport.

The default for an F-35 is to be at something like M=0.9 and altitudes of 20-25kft.

Stealth doesn’t stand still. The latest low-observable US aircraft have lower radar and visual signatures than the previous generation.

It’s not an indefinite ‘lead’, of course, but having decades of experience with LO shaping and materials means you can keep making effective incremental improvements.

Microphone network is mostly used for low speed and high noise Iranian Shahed drones which are also made from composite materials and have very low radar visibility. (For example, Moldovan military recently mentioned that they cannot detect them with their old USSR-made radars).

When one is flying towards you, you hear it from few kilometres away for minutes as it has very loud petrol-powered engine.

In contrast, when you hear low passing cruise missile, you will have just few seconds until it passes over you.

    Russia has some very advanced planes that are barely used.

For a long time they apparently only had two operational Su-57s. Apparently now they have 5-7? This is not a "production" aircraft as we would understand it in the west. Its actual stealth ability is also highly suspect. The official photos as well as photos from airshows have shown some sloppy physical construction that would compromise any stealth ability.

     If you are an army with a few SAM's, what you scare you 
     more: a single F35 coming over the hill, or a swarm of 
     drones so large you had no hope of taking them all out?

For other kinds of targets, the F35.

While your comparison makes sense from a budget perspective, it's not necessarily realistic though. Nobody has the ability to launch that many drones at once and nobody is flying in a single F35.

Also, respectfully, a lot of the anti-manned-fighter arguments boil down to "drones are really good and useful!"

Which is true, but also not something that anybody disputes. Even the most diehard defender of manned aircraft is going to tell you that drones are a huge part of the future of war. And that manned fighters are niche.

Russia has nothing like the F35 and Ukraine has planes too (although not as great). Once Ukraine got F16s they had an impact (even though it's a very old model).

The idea of a drone swarm is science fiction at this time. First, it's not 10,000 drones. Maybe the low quality stuff Iran builds is that cheap. A good western drone will be expensive but also of far higher quality.

If you try to send a drone cloud then they are easily detected and you can just shoot them down. If you send them one by one then they get detected one at a time. A few get through as we see with Israel who dealt with well over 30,000 drones/rockets over the past year... But it took them a year to launch 30,000 rockets/drones. They did very little damage.

You need logistics to send them out big logistics are a big target for an F35. If you do it from far away (like sending drones from Iran) then radars have a lot of time to pick them up and shoot them down. If you do it from close by (like Lebanon) then some might get through but the F35 in the sky will destroy you very fast.

Finally, they all need to fly autonomously which is flawed. You can take them down like ducks in a row. Any soldier with a smart scope can just bring down a drone. Not to mention their deep vulnerability to electronic jamming.

I used to think like you as an engineer. But having spoken to people who actually know this stuff I understood the difference. Yes, there is a price disparity which is why the Israeli army has both drones and F35. Different tools for different jobs. A drone can't carry the damage and logistics an F35 can. But sending an F35 to shoot down drones is a remarkable waste of resources. That's why Israel is working on energy/laser based defense systems which will make a swarm of 10,000 drones completely useless but won't even scratch an F35.