I think the fanrage was because the ship was a K'tinga.
People have the impression that the K'tinga was a refit of the D7, contemporary to the Constitution-class refit.
So, a plain old D7 would have gone down better - but a K'tinga was really out-of-place - and because people take on screen information as gospel in our beloved franchise, there was no way to ignore it - it became part of canon the moment it came on screen.
There is another possibility:
Maybe the K'tinga is an older model than the D7 - but that means it's use in DS9 as a front-line ship, is all the more weird.
I suppose old battleships have sometimes served for 80 years in the Navy, but 250 years of the same hull being refitted comes off as pretty unbelievable.