hmm, I never noticed that but it’s true, you have to delete the keyframes one at a time.
However you can enable the track for writing and selectively re-mix portions of the timeline, and it overwrites your keyframes with the latest settings.
If you want to adjust audio on the fly for one clip, you can do it from the effects controls – which works pretty well – although not using the audio mixer for adjusting audio on the fly is a bit abnormal.
On the Media 100 for example, you can use the audio mixer to adjust clip or track volumes with the same slider, and it goes from clip to clip on the fly. It would be nice if you could adjust clip volumes on the fly without having to stop between clips. Basically you should be able to do the same thing as when you mix a track, but have the keyframes reference the clips.