>>55553500Single-prize cards used to be quite good. Pic related was a fun rogue deck, mostly because it could guarantee paralyze, but 100-150 damage was an absolutely acceptable amount of damage.
However, in two generations multi-prizers got +100 HP for free. The main differentiator between the two is the amount of resources they require to come online. 240 HP two prizer and two 120HP single-prizers are NOT equal, because the latter requires twice the resources to power.
Tl;dr: PTCG designers don't understand how to balance a multiprize mechanic.