People usually concentrate on the monster trio in fights since, well, Oda mostly concentrates on them, but if you look at it, the mid trio was never challenged post-TS unless it was a challenge they could not overcome anyway (Franky vs Bastille and DD Family on his own for example) but when they were shown, they pretty easily got through it.
Franky beat an officer while handicapping himself while his opponent could fight fully, and still won, and in General played around with 2 additional ones, Robin humiliated Hakuba, who can very well be a vet/Vice Admiral in his own right, and Brook blitzed BM at least.
Pretty sure they can take vet level characters if their counter abilities are not a disadvantage (like Oven would be for Robin for example).
And Nami at least does not need CoA, CoO might be useful, but her damage output is extremely high.
Monster Point is huge as well, pre-TS MP humiliated a Rear Admiral level character.