The ODROID H2+ is perfect for one of my applications, with the extra CPU power, second NIC, included real-time clock, onboard SATA and an official case option that fits 2 3.5" drives, and onboard eMMC socket. $120 [edit: plus RAM cost] rather than $35 is a whole other price category though.

Sure but the rpi's can be quite price misleading. If you go pick them up at your local retail store that carries them its frequently a $120 date by the time case, heat sink, powersupply, and disk are thrown in. The base cost for the 8G rpi is something like $70, Then you still have to figure out what to do about the missing RTC, SATA, whatever, for a lot of applications.

So, yes its obvious that the $35 model (which at a minimum is really more like $45 because its not usable without a powersupply and maybe SD card) is sufficient for a lot of things. But its also being wedged into places where its not $35 anymore and in those cases its fair to compare with more expensive boards if those boards come with features that someone is adding a hat or external device for.

That's true for the ODROID H2+ too—you need to add in the power supply, case, eMMC, battery, SATA cables, and also RAM. (I forgot to mention RAM in the parent, so the difference is more like $85 + whatever you pay for RAM.)

at that price range why not just go all the way to mini-itx, when you hook SATA etc you will need a larger case with some cooling space inside, mini-itx seems to be a much more practical option then, a quick search found https://www.newegg.com/p/N82E16813157930 there are many to choose from actually.

or just nano-itx, both are easier to get cases and power supplies etc.

I think we're getting more and more expensive. The Raspberry Pi 4 made a lot of deliberate trade-offs to stay at $35. Going to the ODROID-H2+ means paying another $85 plus (I forgot this in the parent) RAM cost. Then going to a "real mini-itx" board probably means paying for a "real" mini-ITX case and power supply. It'll be nicer for sure but there's significant price creep. Looks like the CPU isn't included either.

The ODROID-H2 Case Type 1 has a fan and space for two 3.5" drives for $20. The ODROID-H2 power supply costs $9.40. I'll be astonished if anything compatible with that ASRock board will match that.