The iTunes program (free, by the way) really is not that invasive, and doesn't require an online account to use with your own collection of MP3's - it can import existing MP3's and WAV's, and can also rip / import directly from CD's. When using an Apple account (free; credit card information only required if you want to manage purchases), the music service can search, identify, and tag your MP3's, or you can specify that info manually.
One really cool feature is if you happen to ever acquire an Apple TV and connect to your home entertainment system, iTunes can stream the songs and video contained in your library directly from your PC. Streaming to Apple TV can also accomplished directly from your iOS device.
To me, some of the biggest reasons to use the iTunes program is it allows you to easily add / remove / organize your apps, sync music & app data files between your iOS device and a PC, sync your contacts, e-mail, and calendars with MS Outlook, and perhaps most importantly, BACKUP your iPhone to your PC so you have a recovery option in case of phone failure, replacement, etc. This feature alone has saved my wife and I some anxiety over the years we've been dealing with iOS devices!
All of these capabilities are OPTIONS that you set one time, including when, where and how you sync, and can be changed whenever YOU decide. NONE of these options require using the "cloud", unless you want to - I do all my syncing only to my PC, never online with the "cloud".
BTW -
You don't have to use any kind of playlist, groups, etc. when using iTunes
or the iOS MUSIC app - just select "Song" (top-right selection option in iTunes, or a quick tap at the bottom of the app screen), and your entire library shows up in alphabetical order, based on the title of the song, and nothing else. This sort / display option remains intact until you change it.
And, iTunes and the MUSIC app both display the album cover, which is REALLY cool when streaming to Apple TV...