They're kind of useless? 20+ cost for a unit you want to drop early for swarmers = no thanks. So, too expensive for early game, and by mid-late swarm stops being an issue entirely since you can drop any of the AOE ranged units that deal with swarm far better. Even the black Samurai is pretty underwhelming. And, yeah, Vanguard Tacticians fulfill the same role Samurai do while also being incredibly useful as a ramp unit.

Anya is basically a usable Samurai who also doubles as either a tank or an actually useful AOE clear, so use her instead.