I don't know if it was ever in specific dialog, but you can overcome a tech, then the other side changes it, improves it, etc. so they regain that advantage.
Does anyone really see the Klingons or Romulans throwing up their hands and saying "oh well, they figured it out, let's give up and become botanists" when it comes to their #1 thing?
The cloaking tech "inconsistency" isn't even an issue.
I agree here. I actually makes a bit more sense they had an earlier version that was flawed. The you get version 2.0 which is the Romulan one, then later version 3.0 which is damned hard to find to the point in TNG it was still effective. But I think its silly to expect the version in use in TNG had never been upgraded as sensors got upgraded all the time.