This deserves to be repeated from time to time:
Strings are not "loud" or "quiet". Basses produce more or less volume with setup changes and strings can be an important component of a setup change. Some basses produce more sound with more tension, presumably if it takes more to get their tables moving, and some produce more volume with less tension. All basses speak the best when they reach their optimal setup.
My bass happens to choke down with tension and open up with less. At a certain point, (tuned down solos), it starts to go the other way. Your's sounds different than mine. If I every buy another bass, this is something that I will focus on so that I have the most setup options.
Also worth occasionally repeating is that tension and stiffness are different things. Perpetuals are ropecore strings and when you take them out of the package, you can feel how flexible they are going to be. More or less opposite of how a ... Dominant, for example, feels out of the package. That is different than tension which is a measurement that I don't have the equipment to do.
Perpetuals may be lower tension than Spirocore Mittels, but that's only part of what you are feeling.