We've seen a number of departures from TOS to TNG. There is a lot that is dissimilar. The fact that Klingons and Romulans are depicted differently comes as no surprise. Is it glaringly so? I'm not so sure with the Romulans, as we get only 2 episodes of them in TOS. They are highly militant and almost like Roman soldiers in terms of strict military code. But yes, a son of a Senator will carry weight more than a son of a pauper. That's true even in the real modern world we live in.
As for the Klingons, they were shaped more savagely in TNG than in TOS. In TOS they are indeed very much like the Romulans in TNG.
Anyway, comparing the two seems rather fruitless, given the very nature of the two series. We got what we got.