Any chance that this can be changed? Almost all the mobs in all the water ranking/explore areas are immune. Do any other rangers weapon progs suffer from this oversight?

Does it matter?

You can still kill all the mobs with ease.

At least my mariner could.

True, but, I wish the prog was more useful in your home terrain.

Marshdwellers have almost the same problem. Almost everything in swamps - resistant or immune to poison, plague (veran monsters also likes to ignore dirt kicks that make 2h dirt kick useless). I think prog makes imbued weapons more useful out of hometerrain.