I think there's many situations where a loud, doomy band can do just fine with ~100W for the bass amp. Along with big, efficient cabs, EQ details can play a huge difference, especially if you're talking about a power trio with just one guitar to contend with. In some cases, you could cut pretty much everything below 70 Hz or so (leave that space for the kick drum), allowing the 100W amp to blast the rest of the frequencies nice and loud, as long as the guitar and bass EQ aren't fighting for the same frequencies, it will be plenty full, loud, and deep.
I've kept up with solid, powerful drummers in loud bands with 90-120 W of all-tube bass amp and done just fine.
That being said, those bands were not full-on doomed, stoned volume-worshipping multi-guitar multi-full-stacks types of bands. And I would never support any kind of blanket statement that "no doom band ever needs more than 100W bass amp power". That's just silly. But for SOME bands it does work.