I think you misunderstand. The diff will rise max with a factor of 1.2 between blocks. So if the diff is 300, the next block can be max 360.
I definitely misread your text lol
This is a decent approach. As long as we don't from 250 to 750 in a single jump, you should see better block times. Additionally, as the difficulty drops back down, we'll get to the point where we're riding a sweet spot where it's not profitable for the miners doing short-term calculations for profit(aka multis).
-Fuse