Sometimes it's worth the effort to try to convince people that their assumptions are off - in this case, making a case that the feat being buffed doesn't need it because it's sufficiently powerful as-is. Now, that does involve 'making a case' (as opposed to just saying "you're wrong.") but that would be a valid contribution to the conversation.
For example: At high levels, Defensive Duelist is very good - a +4 AC only once per turn is still fantastic even against multiple opponents, since it's going to change the result of 1/4 attacks outside of extreme cases. If you've already maxed out dex on your Errol Flynn-based fencer character, it's likely to be the best option (especially if your dm requires you to make all of your attacks before shield bashing). Any change made to the feat needs to account for this or you'll have something that's overpowered (as in, outshines non-rapier builds) at high levels even if it's still a meh choice at lower levels.
Or just remove the scaling and make it +5 (or whatever) regardless of level.