Chrome and other modern browsers tune their memory usage taking the current memory pressure into account. If you _have_ a lot of RAM available, why not use it? On a 4GB machine, Chrome will _not_ use 5.2 GB for 3 YT videos and a bit of GitHub.

How is priority of memory usage managed between 10 different apps using that kind of allocation policy?

I have never seen Chrome starting to use much less memory when memory pressure becomes high and I have been monitoring it many times. There is some GC like behavior releasing a small amount of memory from time to time, but nothing really significant when systems starts running out of avaliable physical memory.

I don't think YouTube videos are really representative of web memory usage, because a significant amount of the memory they take up will be the buffered video content itself