I find it's kinda an unwritten rule of "I set the pace and everyone follows or wipes after which we blame the healer." A good default is double group pulls but it depends on the content. DD and Vale have both hard hitting trash and can't use our nice toys so are kinda forced to limit pulls (when synced) while on the other hand library hard big pulls were kinda expected to get it over with (lore/poetics grinding).

If there's not a lot of aoe dps potential then big pulls are counterproductive. If healer is new or not comfortable doing big then (we) don't. Hell, if you don't want to do large groups it's your choice, not that of impatient dps players. If it's something like deltascape then yeah it's kinda an hp contest for who main tanks (let's ignore the fact vit melding is still a possibility) but that's the exception rather than the rule(s) of gauging party player ability and resulting pace in the instance (especially in random parties with super variable levels of skill).