µ's 5b has always hit every character crouching. The range at which it would connect greatly depended on the character. Against Bang, Hakumen and Tager it will connect at maximum range.
The removal of the lower hitbox on 5b is likely quite literal, there is a low hitbox on 5b, and it's no longer there.
This hardly changes the use of the normal, as 2b was always the go-to tool for poking out crouching opponents.
In terms of a counter assault, the range has near doubled, which is a trade for it now sharing the weaknesses of Litchi's CA.
On the topic of DP RC. The combo never changed, it's ease of hitconfirm was the only difference between versions.
To reiterate: Only by calling out the CA with a low-profile normal will the opponent be able to dodge the hitbox, whiffing at longer ranges is negligible, as the old 6a CA would never have reached to the distance that 5b whiffs at. Losing to hard callouts is hardly something that makes or breaks the tool.