Inferno has very little damage. While it does knock a bit of heat resistance off, I still think hell force is a stronger range 1 weapon (my opinion).
As for demolisher, it has a very awkward range and isn't all that strong compared to other physical type weapons at level 30. While it does do physical resistance reduction, getting your enemy in to the range of that weapon early in the match (which I think is important, as using resistance drainers is most effective early on in matches, in my opinion) may be very tricky. I'd still pick grenade launcher over demolisher at level 30, as it doesn't use bullets, it has a better range and you can use grenade launcher as many times as needed.
However it will be interesting to see how resistance drainers work at lower levels now. Shame they seem to have missed out on lower level energy resistance drainers though
Also I haven't fought at level 30 very much, so what I say may be very wrong
they're just my thoughts to the new weapons