I believe this is a false equivalency. Rogues can use great swords, they just can't sneak attack with them. They need to work harder to get the proficiency, using a feat or MC'ing, but you don't have a rule "rogues won't ever use great swords".
I think it would have been better if druids were given proficiency in light armors and Hide armor, period. You would have the nod back to non-metal armor wearing druids which appears to be desired by the fluff, but they could also gain proficiency in additional armors like any other class through feats or MC'ing.