One key difference between prealms and blizzard realms is the administration. On prealms you’ve got GMs working diligently, while on Blizzard servers they tend to rely on automated systems instead of manual oversight.
Combine that with Official petition for SOLO Rated Que - #176 by Bewarê-frostmane and you’d just get a recipe for disaster if they don’t properly separate it.
Read the links above. It’ll help you think more of the ripple effects.