Not necessarily. I didn't have any trouble believing the Klingon ships we saw on "Enterprise" were less advanced than the BoP's and cruisers we saw in the 23rd and 24th Centuries. Even the NX class, if you look closely enough, the metallic plating looks a bit more primitive than the starships of later centuries.
I think it would've been doable to create something that looked like it preceded the BoP.
Oh, OK...I see what you mean. You just had trouble with the 22nd C version of the Romulan BoP. I can understand that. But I think the problem lies more with the TOS BoP more than anything. Because if you look closely at that one, it wasn't much different than a Federation ship with inverted warp nacelles, and a painted bird on the hull. I see what you're saying, but again, TOS was a victim of its own time. I mean, Hell, the original pilot, "The Cage" was filmed in B&W...that's how old it is. The whole series was shot on a shoestring budget , and their model making suffered because of it., not to mention the over-all thought process of what spaceship looked like back then with all the cheesy sci-fi then. TOS came about about a decade too early. Had it been a late '70s production and not a late '60s production, things would have been quite different. And when you look at the Galaxy Class of TNG, I'm surprised they came up with such a radical design in the mid-80s in the middle of the Kirk-era Movies. Coming off of STIII and IV, with the intro of the NX-2000, I would have thought the next logical step would have been something like the Ambassador Class.