If CBU3 couldn't add anything meaningful skill outside of 2 min burst window.

Then why not shorten the period between burst window, like from 2 min to 1 min burst window?

So which means,
120s CD skill action became 60s CD,
60s CD skill action became 30s CD,
30s CD skill action became 15s CD,
45s CD skill action became 22.5s CD

It won't help a lot, but it at least ease the pain of current 2 min burst window design.
Not to meantion, 1 min burst window is much more easier to recover from screwed up and misplay.