There's a couple of things I feel get neglected in these conversations every time they're brought up.
Brand new tanks pre-50 leveling dungeons could possibly be missing some of their Role Actions... and Tanks not knowing that Arm's Length can be used as mitigation (especially for big pulls) is unfortunately super common. Like I've still had to explain to Tanks in SB and ShB leveling dungeons what the additional effect of Arm's Length does... So I don't expect brand new tanks to pull big in pre-50 dungeons cuz they really do lack the tools. However... the inverse of this are Tanks that are level-sync'd down via roulette queues, because Role Actions are always available once unlocked regardless of sync'd level. So I tend to expect more from a level 50+ tank that got thrown in to Satasha or Coppbell or Tamtara... because Reprisal and Arm's Length can do quite a bit to trivialize big pulls.
post-50 leveling dungeons, I seem to notice a lot of tanks don't properly use their invulns as mitigation... still reserving them as "panic buttons" for situations that will rarely ever arise. There are several pulls in the leveling dungeons that I think are made way easier when opening with invulns to soak the most amount of incoming dmg. However, this does usually require knowledge of the dungeons layouts to maximize of course.
Those caveats out of the way... in general my only expectation is "2-pack minimum" and not necessarily wall-to-wall pulls. The thing about that though... is most expansion leveling dungeons only allow 2-3 pack pulls before gating access anyway. Actual wall-to-wall situations in the truest sense of "boss-to-boss" pulls are rather infrequent post-50. Standouts I can think of off the top of my head are between first and second boss of Doma Castle and TWO wall-to-walls in Mt. Gulg (before first boss and after second boss).