Playing a hunter and sometimes having mobs reaching me in melee, I find myself able to outrun them quite easily and get range without having to wingclip them
Now I know different mobs have different speeds, but still, It seems still easier than what I can remember
Slower? Man i was farming some level 17 plainstriders at barrens and when they drop to like 10% they started runing like mad lightning even on mount u wouldnt outrun them
It really is just that different mobs have different speeds.
Most starter zone mobs have less movespeed than the player.
Outside of that, it can vary extremely.
Usually they are at least slightly quicker than the player, but some mobs have basically permanent sprint (i.e. Murloc Coastrunners in Westfall).
You can easily get a feel for it, by standing still at max range, pulling something, and seeing how far your autoshot timer goes (would need an addon tho to be precise) before the mob reaches you.
edit: + what Itaa wrote; low hp mobs run slower (not just when they flee).