It is unclear if tainted dust is supposed to be like redstone or like gunpowder but I think its just both, especially because you can't use it like redstone

Tainted dust is really just a block light decoration and I don’t think sickened creepers should drop it

I see it more as tainted redstone dust than tainted gunpowder. A redstone use would be really cool tho. Maybe it has a longer circuit length