And I know what I'm talking about because I thought about doing something like what you propose for a while, and I concluded that I'd never be able to beat Behringer. I'm not saying it's impossible, it's just not easy and Behringer has a lot of merit in being efficient at producing these synths.
If there is any other merit to what you're looking to do, and you can float the cost, you can make a thing happen and see if it's too niche for Behringer: if it's that popular, you'll get a knock-off for pennies on the dollar and your best bet is to position yourself as the original, and accept your market got ate.
I don't think Moog is ONLY selling out because its Minimoog got cloned by the Behringer D, but I've owned a Behringer D and soundwise it wasn't half bad: many decisions made were in the service of the thing actually sounding good, at least in the revision I had. I own a Moog Sub Phatty and swapped out the side panels for aftermarket wood ones, because it had the 'sticky plastic' issue, and the octave switch for octave 1 ain't working. The flagship Moog One synths have had some issues. This sort of thing is brutal on a small business… they're paying more for their parts and labor, but they'll run into the same issues that Behringer or any manufacturer will.
You won't out-Behringer Behringer. It's exactly the sort of T-Rex you don't want to battle directly. There is nothing stopping you from being a small mammal scurrying about making stuff. Come up with a business model that bootstraps and does what you need, and don't attempt to get capital that would demand a 10x return while knowing Behringer exists, as you can't have a 10x return at all, ever. You can probably still make stuff but you have to design the business, not just the product.
What this means: with a Eurorack module, you don't need a case or power supply, since that's provided by the Eurorack "infrastructure". All you need is a "front panel" on your module as well as certain connectors, and probably one of the cheapest ways to build such a front panel is by manufacturing another PCB with the right size and the right holes. You can do that e.g. at JLCPCB, for <1€ per front panel. Building the synthesizer is similarly easy: design the circuit, create a PCB design that uses modern technology and SMT machine assembly, and you can get even "complex" designs manufactured cheaply, to the point that you can even beat Behringer yourself. After all, you don't have to live from selling such modules, and your development time is "free". And the best part: once you have a working design, you can get as many more modules manufactured as you want, for significantly decreasing prices if you manufacture them in slightly larger batches.
To give you an idea, I recently built a small PCB with "transistor ladder filters", but since they are small and cheap, I extended them and made the feedback path voltage controlled and also added a VCA directly after every filter. A PCB with 8 of them, manufactured and assembled at JLCPCB, cost around 30€. For completeness, this was for a 8 voice polyphonic Eurorack synthesizer module, which means this PCB didn't need any knobs/buttons/jacks/displays. Meanwhile Behringer sells a single "Moog VCF" in Eurorack format for >100€.
Also,there's a lot of very good software used by many people that came from some person's personal github account. Hobbyist can and do compete favorably with commercial software all the time, but of course it's not as easy to make a living that way than it is to just put something out there that's useful.
Also you underestimate economies of scale behringer can employ, I'd be surprised if you could get close to their price.
You can look at various DIY stuff and you will probably notice that getting stuff DIY isn't all that much cheaper
I'll throw you an example:
Maths, which Behringer cloned, costs ~$300 fully assembled
Befaco Rampage, which is pretty much equivalent to Maths, costs $185 in DIY kit.
Behringer Abacus is $100
They are basically selling them at price or below what DIY kit would sell, and not that far off "cost of components"
Behringer has impressive scale, but honestly I think for PCB manufacture and assembly, JLCPCB probably has them beat -- and any random hobbyist has access to JLCPCB.
The cost of Maths and Rampage has more to do with having to earn enough to pay all their employees and make a decent profit that the actual marginal cost of manufacturing one more module. Maths is very popular, but it's still a fairly low-volume market.
I think one thing it would be hard to compete with Behringer on is enclosures. But maybe that doesn't matter; a Neutron/Proton clone wouldn't necessarily need one if it's a Eurorack module.