Omnikeys (like mid-80s Zenith, etc. keyboards) are sturdy because they have a pretty thick plastic top, and a metal bottom. Otherwise, they’re internally similar to other Alps boards, with a steel plate and a PCB.
An Omnikey with your favorite Alps switches swapped in and some Alps PBT dyesubs for keycaps is basically the pinnacle of IBM PS/2 101-key ANSI layout Alps keyboards, outside of some custom board built from scratch.
I don’t think it’s too easy to directly compare it to IBM keyboards. It’s probably easier to break than any of the IBM boards if you start smashing it into rocks, pouring liquids into it, dropping it from second-floor windows, etc. Should still be a pretty effective weapon in hand to hand combat though.