Does iTunes library stored in iCloud count in 200Gb plan? Music uses up most of MacBook and iPhone storage...

Music is not part of the normal iCloud storage. If you want your music in iCloud you have to subscribe to Apple Music or Match. The exception is iTunes Store purchases which do not count against any iCloud plans you have going but are theoretically always in iCloud too.

cancel your storage if you do not need it... you can add your music to icloud drive for storage, not so effective for accessing it on a regular basis.

As for useless, anything you buy and do not understand seems to fall into that category, if you pay for 200GB pf dropbox seems it would be just as useless, not sure it is an Apple issue