Muddy is certainly not desirable for professional DJ gear.
This is all totally subjective as always but as much as I love my Prime 4, I really dont think the sound should stay as it is. This also goes for any audio unit from any audio brand. Constant improvement should always push the best sonically from the unit and improve features because this is the units basic function. To provide professional audio to people dancing. Getting the basics right is fundamental and sound is the bare minimum thing we should (mostly) agree on. I visit many forums from different manufacturers and the market leaders rarely debate sound like we do here This says to me that there is an issue somewhere.
As said above, each person will see the sound as subjective and this is only my own personal opinion. On an A > B comparison the sound isn’t at £1.5k. I have a controller I just can’t use on XLR output due to how lifeless it sounds, yet on the RCA out it’s not bad at all.
A few DJs often state that the people on the dancefloor don’t notice sound but any gear is purchased for how fun and enjoyable it is for the DJ to use. I work for four to five hours a night, seven nights a week for five months with my DJ gear and it has to sound right to my own ears and not create fatigue. Drop this P4 on RCA out and I can go all night with it… but that’s a workaround. I shouldn’t have to run it into a second mixer when it has it’s own balanced outputs on it.
At the end of the day there is no right or wrong answer. The sound is pretty much perfect for some users yet muddy or harsh to others but our individual circumstances have a big role to play here. Some users are club DJs, some are mobile DJs and some are bedroom DJs. Some bedroom DJs will have never heard their gear played on a finely tuned club system, only through a pair of KRK monitors or a Hi-Fi (possibly by the RCA out). Some mobile or wedding DJs will have only have ever heard their gear plugged into their powered JBL or Mackie sound systems. Some DJs will have used them in a club with various other bits of pro kit in the booth. This is where an A > B comparison can easily be made and this (I feel) is when the sound characteristics can be exposed.
What is flat with no dynamic range to some is nice and warm to others.