Indeed, some production lines have wierd ratios. Chemical to Tel is 4:3. Chelt to Rastar is 5:4.
But in practice this doesn't really matter. You will be loosing random resources in storage fire events, from haulers getting killed, from factories idling for too long. You can also gain a fair amount of random resources from loot now.
It's likely that there will be some logistical inefficiencies causing further imbalance over time before you finally notice and find the time (mood) to fix them hours later.
There will certainly be times when some factories stop producing during your playthrough. Given the limited UI there is almost nothing you can do about this and it's better to even expect it. Mayhem 3 is like the worst economic game you can choose if you want everything working flawlessly all the time and can't stand situations which require you to adapt or change your initial plan or setups.
Maybe you build more and more factories but forgot to also ramp up your Agent count and end up with too few ships to keep up with the hauling. Maybe your worker range and Agent travel times are too high after a jump beacon got destroyed. Maybe you made a dumb mistake while setting up your Agent jobs, or forgot some of them entirely. Resources might be piling up in the wrong outposts. Or not get hauled away from factories at all. There will be empty factories flashing yellow. Full factories which don't even flash to garner your attention (full factories can only be identified if you specifically look for them).
Your economy can become a fairly well oiled machine. But it's unlikely that you play to a point where it doesn't need to be oiled or expanded at all anymore. And during your pursuit of creating the most well-oiled economy, countless problems will slip your attention. Embrace the change! I think in the end you should be prepared for imbalancies in your production chain and plan accordingly or the game can become very frustrating. A Chelt factory only producing 4/5 of the resources for a Rastar farm will be the least of your problems.
Now imagine you put your entire crystal production in one sector. This is tempting because it simplifies logistics. But it can certainly set you up for disaster if you stick to this playthrough long enough. Could you still haul your crystals to the other end of your empire without jump beacons? And what about some enemy occupying your sector? Could you even produce enough crystals elsewhere if you couldn't reach these factories for the time being?
Creating redundancy for situations like these tends to become the real issue after some time. And it feels quite rewarding to develop your very own solutions.
At least to some crazy niche fanbase with a knack for tycoon games
****, it became a long essay again, so:
TLDR:
1) Mayhem 3 is at least 51% an economy game. (more than Mayhem 2 in my opinion)
2) Managing and expanding your production will likely be a neverending story. The UI is cumbersome, but you generally don't need to act quickly either. (think "Factorio on Valium")
3) Expect problems which can force you to adapt and change your setup later on. You should evolve and treat your economy like an increasingly complex organism. Eventually you loose track or your nerves and stop playing. Or your economy/empire ends up as a very rewarding personal creation. Then you keep playing and most of it gets mapped in your brain which also counters the bad UI.