There is a pretty good defense against daggers in and of themselves: gear/prep for STR/DEX (and/or cut down their dex as well). Also think about wearing a shield to cut down on concealed's if applicable to you.

However; STSF: there is absolutely no way you would want to ~not~ take this as an elf/drow. It might as well be hardcoded into the build these days. And unlike a greeting bash spec, it works agains pretty much everybody.

Fighting an elf/drow with and without this legacy is just night and day.

I think a simple solution would be to make the charges build a little slower so that they a) don't fully charge during one fight, and, b) are lost if you kill them/they die. I don't see anything wrong with the legacy being pimp for a savy player who can use tactics to build the charges over a bit of time, but having that thing fully charged after one fight can be a bit ridiculous at times.