Unless I’m misunderstanding things, you’re proposing the exact opposite of what Guillermo was suggesting. To summarise (and also as a double-check that I actually understood you correctly):
Guillermo’s suggestion: on keyframe insertion, deselect all keys, and only select the newly-inserted keys.
Your suggestion: on keyframe insertion, do not touch selection of existing keys, and keep newly-inserted keys deselected.
Do you have a link to that?
Blender has always selected the thing you just created. This works like that with bones and with objects, and now Guillermo proposes to do the same with keys.
Earlier Guillermo and his colleagues also suggested: When selecting a key, automatically jump the playhead to that key so that you can click a key and immediately drag it up/down and see the effect. I think that plays along nicely with only having newly inserted keys selected.