It might still be valuable to kill swarm engines, such as Lieutenant Von Herst, Jacques, Grand Inquisitor Helveed, Keldar,... before they generate multiple tokens.If you face a deck not having a valuable target (e.g. many swarm decks) the value of heatwave is heavy limited.
It is convenient to banish a swarm enabler such as the Plague Maiden. You trade a 10 provision card for a 10 provision card, plus you damage your opponent strategy (no swarm for Chimera, Bone talisman, Glustyworp, etc...).
If you play against a swarmy Lippy deck with Cerys, banishing the card will give you 4 points in this round and negate 8 points carryover in the next rounds.
Banishing Gezras of Leyda or Brouver Hoog, once the opponent has swarmed the board with elves / dwarves is also great.
I also think that many swarm decks are not purely swarm, but have some sort of tall finisher (Glustyworp) or tall bronze support (Fallen Knight).
Really, it's hard for me to think to a situation in which I blamed Heatwave for a loss, because it didn't find enough value (even in an unfavourable matchup).