MM5 as you said ATM "affect a handful of testers" and it needs to grow and expand. MM5.0 is builders block like LEGO and I've seen MM grow from 1.x to 5.0 and what can be made with single brick wall.
To bring order there must be a chaos to put in order.
It is not unknown to MM that progress is seen from build to build.
Addressing "any apparent areas of confusion, like filter|search or increased consistency between the modes ... IMO" is priority and must be addressed ASAP along with greater stability.
Adding new features in MM5 is much easier and open than any earlier MM, take for example All Nodes where in MM4.x it is core feature and MM5 allows it to be separate script that can be easily changed/fixed where instead in MM4 CORE app needs to be recompiled. But if MM4 was perfect there wouldn't be MM5 right?
And for your worries just look at past and differences from MM2.x -> MM3.0 then MM3.0 -> 3.2 and 4.0 -> 4.1 https://www.mediamonkey.com/news/2011/ and you will see that Version number doesn't mean we are done, but barely that we are just starting new chapter.