Something useful. You can check it here ;
https://www.loudnesspenalty.com/

Online streaming services are turning down loud songs.
We all hate sudden changes in loudness - they're the #1 source of user complaints.

To avoid this and save us from being "blasted" unexpectedly, online streaming services measure loudness, and turn down music recorded at higher levels. We call this reduction the "Loudness Penalty" - the higher the level your music is mastered at, the bigger the penalty could be. But all the streaming services achieve this in different ways, and give different values, which makes it really hard to know how big the Loudness Penalty will be for your music...

Until now.

Simply select any WAV, MP3 or AAC file above, and within seconds we'll provide you with an accurate measurement of the Loudness Penalty for your music on many of the most popular music streaming services, and allow you to preview how it will sound for easy comparison with your favorite reference material.
Your file will not be uploaded, meaning this process is secure and anonymous.
https://www.loudnesspenalty.com/

Why Does Bouncing My Master at a Specific LUFS Level Help my Music Stand Out on Online Platforms?

Spotify and Youtube stream audio at around -14 LUFS. If a track has a loudness level of -9.5 LUFS (like AC DC Back In Black) both streaming platforms will decrease the volume of that track to around -14 LUFS.
https://www.masteringthemix.com/blo...dio-for-soundcloud-itunes-spotify-and-youtube

 

The real question is how they got the AC DC Back in Black track in -9.5 lufs, lol...probably a new re-mastered shit.

 

In theory... if the end result is that every track is normalized to the same level I'd think it didn't matter.

Of course, theory and real world actuality are usually different things.