Not entirely, while breachers are best suited to ZM and have a plethora of bonus/traits that keep stuff like cold void from hurting them you do end up paying a hefty premium for them, from memory a moderately tooled up 10 man breacher squad without melta bombs is somewhere around 225-240 mark, for a few extra points you could get 2 basic 10 man tactical squads, certainly less survivable 1v1 but quantity is a quality of its own.
Assault marines also have their benefits, namely superior movement, while not without risks due to difficult terrain it is minimal and "practically" non existent with a feel no pain, one of the things that I've seen trip a lot of people up is they send there units down a path in ZM that would effectively leave them doing nothing for the game, a 12 inch move mitigates that and gives you an advantage to close the distance on objectives etc and also have access to squad wide meltabombs which are useful. Though it is debatable how fluffy jump packs are in ZM, then again the white scars also race their jetbikes around their ships so there is that.
alternatively there's a dozen other troops via rite of war that are lethal in ZM, looking at you terror squads, or just straight up improvements on the existing choices.
personally I tend to either go cheap with the tactical squads to either take more toys else where, out number my opponents or I go with moderately tooled up breachers, which for me is usually 10 with 2 meltaguns, artificer on the sarge, a meele weapon of some description and a cyber familiar if I'm using them in my Iron hands army .
TL;DR yes they have a place it all comes down to what you want to focus on cheapness (Tacs), mobility (Assault), durability (breachers), lethality (anything other than breachers)