I believe her presence in cutscenes is fine, it’s the running commentary she does during gameplay that I deteste, especially when she introduces the targets whenever you look at them, thus talking over important dialogue you’re trying to eavesdrop on.
In the old games, Diana barely spoke and because of that it was nice to hear her - especially during a mission. But now that the airwaves are saturated with her unfunny comments, the value of hearing her is decreased. Less is more. Perhaps the answer is reducing her dialogue (can you do that if you reduce the opportunity hints setting?).
I’d also like Vivienne McKee to voice Diana again, but her replacement doesn’t ruin it. Even if she does now have a stereotypically posh British accent. McKee’s delivery was much more business-like whereas the new Diana seems to be very whimsical in her briefings, contributing to the more light nature of this game.