I have job as well. Can play only about 2-3 hours per day, and even on weekends I can’t spend entire day doing absolutely nothing but playing WoW.
You just have to accept the fact that each specific ruleset have different populations, with PvE being the most populated.
I’ve picked RP-PvP because that’s the reason why I play WoW Forever, to enjoy the RP aspect of the Warcraft MMORPG, and the population is always moderate there.
Never felt neither empty nor overpopulated. Only downside is that it’s already getting filled with people who don’t follow RP rules, and play there only to avoid overpopulated zones.