Blanket statements like that doesn't hold up in this world. There are 1 and 2-driver IEMs that sound good and many-driver IEMs that sound like trash.
Cases in point, Truthear Zero:red (dual dynamic) and Etymotic ER4XR (single BA). Note that the truthears require a very low output impedance headphone amp to sound right, but I'd pick either of them over Shure 535s or 846s, even if the Shures were free.
Unfortunately, for every good-sounding IEM, there's 10 examples of junk. Some of them are super hyped online, and I can't figure out why. FWIW, everything I've heard from KZ and Shure winds up in that box...the Shures can be usable, but I wouldn't call them good. I've tried a few KZs, and they all sound really scooped. IDK...maybe they've gotten better. It's been a few years.
All the other comments about making sure you get a good stereo mix and most of the advice in Cooper Carter's video are good things to try.