Normal and swamp rain dont really make "wet" on enemies , the wet debuff is that really kill surtlings
This can be tested with frostner or frozen arrows : most show u yellow numers ( weakness ) because make real wet on enemies ( makes them swim and next hit them ) do that , but rain didnt , them keep showing white numbers
Thats why surtling dont die for rain but them nearly blow up when touch a little body of water