Is Apple storage management bad or is it my devices acting up?

I have used Apple from iPhone 4 and up until now, the issue has been the same, storage management… Apple is failing on this front… I have deleted all media’s on my iphone to free up space and all it does is increase the size of system data… Somehow I feel like all the data we delete is moved to system data and take up more space… As if that’s not enough, Whatssapp storage ballooned from 7.5Gb to 10.66Gb after installing an update…

Recently I bought a new USB, copied audio files from my MacBook to windows… Came back and deleted the audio files from the USB on my MacBook. The files were deleted, storage not free or released… Used the USB on my android stereo, the deleted audio files played on my stereo even though I could not see them… storage management has been a headache for me for a very long time…

What am I doing wrong?