Yep same issue here.

SD needs to fix the tech Preqs so the shortbow and longbow can only be researched after the fortifications/archery/range stuff is "discovered". That would help reduce the confusion of being able to design units you can't build.

Have heard that it doesn't work at all for kingdoms. Is that true or can I research the line and enjoy?
I have the requisite archery-tech but can't build ranges (from master archers trait. What a surprise...). Is researching the rest of the prerequisites enough or do I need advanced archery on top of it?
Not that its a big impedement thanks to the new awesome power of longbows and even shortbows+heroes.
Who needs a paid army then? (Works better than ever...)
But still not the most fun thing to be barred from building huge armies of archers / horse archers to see the wildlife suffer and dump the soon to be millions of gildar into something fancy for large-scale testing.

How about you can have saved custom units that you can load in any game, but ones that are the wrong race or that you don't have the right tech for are listed in red text in the Design Unit list with the text why you can't build them.  Only units you have the pre-reqs for would show up in a town Train dialog.

What do you think?

Best regards,
Steven.