i see this VERY often from hunters... i go at a good speed... chain pulling to a point that i basically pull everything between two bosses (if the healer can keep up or i know i don't need him)

if i'm not pulling it has a reason... either i'm waiting for runes or the cd on keg smash before a boss pull... or waiting for thunderclap to grab aggro on the pack i'm pulling... OR i spotted that the healer is at <5% mana while i'm on a char that still needs one

other reasons would be: the trash is fucking dangerous if you pull too much (everbloom before the mage boss... / ubrs before the dragon on the bridge)

i don't need a some idiot pulling stuff for me... you're waiting 15+ minutes for groups... you can afford waiting that extra second and WILL let you die if you pull (even if you're my healer)

this is not a case of being on a "high horse" but a simple case of respect towards your group... as long as the tank doesn't wait way too long between each pack you're probably SLOWING the run with your pulling...
sometimes by spreading up trash because the tank can't take aggro immediately
sometimes by wiping the group because you thought you're too good to get that ticking debuff that the mage trash in everbloom applies (spoiler: you WILL die... your healer WILL die... the other dps WILL die... and probably the tank too)
sometimes because the tank can't stand not being in control of what is happening and leaves to get a new group like 5 seconds later (having control separates good from bad tanks... if you take it away from the good ones they are pissed)

i could list shit here all day... but since most people with your mindset are not patient enough to read this here is the TL/DR:
DON'T PULL... IF THE TANK IS NOT BRAINDEAD THEY ARE DOING WHAT THEY DO FOR A REASON and don't need some shitlord pulling the whole instance for them