Hey mate,
thank you so much for taking the time to write out such detailed, constructive feedback! Getting through a full prestige run on a prototype means a lot, and you hit the nail on the head with your feedback.
Ash & Incineration: Right now, those mechanics feel very wonky, I agree.
The grand vision for the game is Collect > Incinerate > Factory Automation. Ash is going to be the raw material used to build and fuel a pure, Shapez.io-style grid automation mini-game where you build production lines to geoengineer the planet. Returning it to its former beauty, so of thing.
Slow Progression & Shop Ordering: You are on the money! The early game grind is currently too stretched out, and the upgrades shouldn't let you buy out of order. I’m refactoring the shop so that higher tiers stay cleanly locked and hidden until you've bought the previous versions. I'm also trying to work out how to do pre-requisite upgrades (without going down the full Skill Tree route - any suggestions would be very much appreciated!
Drones are too crap: Yeah, they suck 😂
I'm thinking of removing the "recharge" which I pretty much adapted from Leaf Blower. The current basic drones are getting a massive overhaul. I am currently porting Boids algorithm for the trash drones so they behave like an intelligent swarm. Instead of just wandering aimlessly, they will coordinate advanced clean-up strategies like pincer movements, line sweeps, and boxing/pushing trash piles together in tandem.
But right now I'm struggling to get the Boids to work with formations and military-like manoeuvres!
I am hoping to bring that into the game soon.
Stats Screen: Adding a dedicated stats tracker is a fantastic idea to help you keep track of your efficiency, especially once the automation kicks in.
I actually have a "god mode" debug overlay locally (see below) that lets me jump ahead (which is probably why the pacing is off 🤔), spawn tons of bots and generally just push my code to absolute limits. I want to bring some of that for everyone! 
Out of interest, what sorts of stats should I show? Trash-per-second, Totals, playtime etc. Maybe a line chart of income (collected trash vs. incinerated vs. used for component construction)
Anyways, hope this explains a few bits and bobs I have in the works. This is my first game, so receiving feedback like this is incredibly motivating and helpful to my own roadmap.
Thanks for helping me make it a better, more relaxing experience.