You are addressing a different question.
The question 'Is it loud enough for me?', is a personal and, quite frankly, uninteresting one. For some, they don't understand why a little Phil Jones combo wouldn't be enough 'to do any gig'. For others, they complain about their bridged thousand watt power amp into two 410's not punching enough. Neither is right, neither is wrong. This is why some think guys who carry around lead sleds and huge stacks are idiots, and others think that those who use small, lightweight amps are 'compromising their tone'.
The other question is a bit more quantitative...'which amp is louder'. However, there is a qualitative component here also, since part of 'volume' has to do with 'volume across the entire frequency spectrum that you are interesting in'. A 20 watt guitar tube amp can pretty much bury any bass rig out there since it is only reproducing, in the bass dialect, upper mids and above. If you like a Jaco burp, an amp that is somewhat attenuated down low can sound ridiculously loud, and actually 'louder' than a more full range, evenly voiced bass amp. If you are dub player, you might experience that amp as thin, lifeless and soft.
I continue to be amazed at the confusion between... 'how loud is the amp?' and 'is it loud enough for me?'. Two very different questions that almost always result in different answers

The first question is again, personal and uninteresting IMO, the second is relatively clear cut (but not completely... and of course, a 'louder amp that you don't dig' is a clear 'fail', just as much as an amp you love that will not adequately generate the tone you dig at the volume needed).