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.