Parting shot: ENT is between modern technology and TOS. Shouldn't a ship designed between those two time periods reflect that?
Modern spacecraft:
-metallic paneling
-tech greebles all over the outside
-rounded portholes
-rocket-like RCS thrusters
-structurally reinforced design
TOS spacecraft:
-round bulbous bussard collectors
-mostly featureless design
-thin, physically unsound design (like pylons)
-ambiguous hull plating
To paint it in another light: It seems that out of love for tacky '60s design, people insist that because something is older than TOS, it should inherently look older than '60s. Perhaps the crew of the NX-Ent should have worn Victorian era clothing? That would be roughly correct for one hundred years before the '60s, wouldn't it?

Red line is current ENT to TOS. Blue is hypothetical "more primitive" design aesthetic.