Honestly, I would rather tanks just pull what they/the party can handle, even if it's one group. In most instances pulling wall to wall is totally fine. I've literally never died to a mob in any level 90 dungeon, for example. There are some dungeons, like Hollminster Switch in my experience, that seem to challenge a lot of people. Even then, I've had tons of runs that went fine in there pulling wall to wall. So, if the tank feels like they can get it done with the party they're in and they've done it many times before, go for it. If they feel uncertain or are new to that instance, I would rather they pull smaller. It's way more inconvenient to wipe than to just do smaller pulls, imo. The tanks that take on more than they can handle twice in a row are the ones that I really dread, not the ones that pull small. I've had tanks die to three or four mobs but never just consider going smaller and it's such an unpleasant experience. It drags on forever and the time spent running back through the half empty dungeon is much more boring than longer time spent fighting smaller groups. But as long as the pulls are a manageable size for the party you have, I'm basically fine with whatever.

To be honest, though, I use the duty finder for roulettes and general leveling very often and I rarely have terrible experiences. I feel like sometimes people exaggerate how often things go completely sideways in there.