Mindustry

I first played Mindustry some 8 years ago on a phone. It wasn't actually that bad as a mobile game, but it was rather bare-bones. It was clearly part of the first wave of Factorio clones, and as a small indie game didn't really have much to compete with Factorio even when it came to Steam a couple years later as a PC game. But recently, while looking through what the highest rated RTS games are on Steam, this came up in the top 5. At first I thought, "this must be mislabeled - it's not really an RTS game any more than Factorio is", but I took a look at it, and it's clearly gone way more in the direction of an RTS, and had a whole lot more updates over the years, being seemingly in constant, albeit slow, development.

The factory-building elements are still simple - undepletable resources, single-lane conveyors, and only a couple of production steps from raw resources to a finished product. But what is the finished product? Well, raw resources themselves can be used for manual construction or ammo for turrets, but otherwise they usually make units. Or upgrades of units. Lower tier units building into higher tier units is probably the most complicated production step in the game, but even then it's just feeding a bunch of mostly-raw resources to each constructor.

I would say the belt management is a much larger challenge than setting up the right production lines, but I can't say it's as enjoyable. The RTS aspect also enforces a very strict time pressure, meaning you have no time to plan your factories, calculate ratios, or anything of the sort. This is a huge detriment to the factory-building aspect of this game. Similarly, while this game has the most RTS elements of any automation game I've played, it's not actually a good RTS. Perhaps due to compatibility with phones, the unit controls are quite bad. And for whatever reason, the AI is really bad, failing to display any semblance of intelligence beyond beelining their units into your core, even if that means rushing past your defenses and never building up a larger force to attack with. Maybe for that reason, to give the AI a fighting chance, most units in the game can actually ignore your walls and turrets and just go straight over them. It also can't understand the concept of linearly rebuilding its base, and instead rebuilds random blocks that have been destroyed.
While the current system with building units makes it viable as a PvP RTS, I think it would have found more success as an automation tower defense game. Either closer to Factorio, but more combat oriented, or closer to Creeper World, but more automation oriented.

Much like many games before it, Mindustry has tried to combine two different genres of games, but instead of managing to combine them harmoniously to something greater than the sum of their parts, what we're left with are a rather poor factory-builder and a rather poor RTS. On the bright side, it is available for the lovely price of free if you go over to its Itch site. It's also open-source, so that's cool. In fact, here you can see all the places you can get this game. Would I recommend getting it? Not really, but it's not that bad. For something completely free, it's actually decent, so maybe try it if the price is an important factor.