Hmm - the OB-6 definitely weighs much less than my Roland HS-60 (Juno-106S, with speakers) and, by memory, the Oberheim Matrix-6 keyboard, so–lacking a transformer inside–I wouldn't expect there to be much to reinforce for ... or am I missing something?
I don't see torsional flex as a bad thing in something that's eminently lightweight–but I'd be very concerned if it was something heavier and bulkier, e.g., an OB-Xa (which I have seen).
AFAIK, the construction is similar to my Mopho SE.