How important is loudness for the success of a song?

hey folks, so something has been bothering me ever since the demi lovato's lead single "fast" from her new album came out. without going into what the song was like, (i did like it) i went to turn it up and it just wouldn't turn up. it wouldn't get any loud.

so, the lead didnt do as well, and knowing audio stuff the way i do and how "louder is always better" term is used in the community, and the whole loudness war thing. i converted the official video to mp3 and looked at it in reaper. the chorus was peaking at around -7-8 db peak. with a stray peak going to -3 something for a split second only once in a song. the lufs integrated showed at -18. like so much headroom.

compared to another song i was listening to at that time, a little more by ed sheeran, it was basically trying to blow up my speakers, i ripped it too and the peaks were crossing 0 with some hitting +4 db. now its not the most official way and it wouldnt be +4 actually, considering the conversion site is adding a few db's to that. the demi song should be even quieter. which is just, breaks my brain. if you compare it to the youtube music version thats a fair bit louder. as it should be.

question is, its well known that most services turn things down but dont turn them up. and with everything else so loud. having your official music video, lyric video turn up this quiet. its bound to hurt the streams. question is how much. how better would it have performed if it was reasonably loud. the song aside, it almost feels intentional, if she's not cool now or whatever, is owning her masters or the labels not having much stake in the success of the album. yk, you've shined enough, make way for others type of thing. i don't see how any competent engineer would let it slide through and wouldnt notice the levels. any thoughts on this?