Dessert Nomad
Adventurer
Also, if you want an example of a martial character messing with the movement of enemies through tight corridors, a fighter-type with Polearm Mastery and Sentinel can shut down enemies much more effectively - an op attack as they enter his reach will drop the first giant to zero movement, and leave him blocking the others. The giant can't just dash to get out of the way of his fellows, as sentinel drops his move to zero for the rest of the turn. And the other giants can't use 'move through an ally's space, because they only have at best 10' of movement left when they get to the sentinel-stuck giant while they'll need at least 20' of movement to move through two friendly spaces. That does put a melee combatant into melee with one enemy, which is kind of his thing, but doesn't actually use up any resources, and only requires the melee character's reaction, not his main action or a counterspell.
10'x10' enemies with 30' move rates in tight (for them) corridors are just going to have a bad time in general.
10'x10' enemies with 30' move rates in tight (for them) corridors are just going to have a bad time in general.