For myself anyway, I have never seen a player take this feat for their characters--or frankly even talked about considering it.
Compare it to Arcane Deflection. Although it only adds a +2 static bonus to AC, it also can add instead a +4 bonus to a saving throw! That is pretty huge IMO.
Now, I think Defensive Duelist as a concept has total merit! I also think if the buff to AC was equal to your attack bonus with the weapon you are parrying with, instead of just your proficiency bonus, it would be better. I mean, it is a feat after all. They don't have to be OP of course, but for most of the levels of play a +2 to maybe +4 bonus against one attack, at the cost of your reaction, just isn't really that great as I see it.
Since you think it is good enough as it is, great! But apparently a there are players such as the OP and myself, who don't. I like the idea of adding something more to it, or buffing what it already does, or make it a half feat and give it a +1 DEX bump. Then I would probably see it taken a time or two, if for nothing else than the DEX bump.