So either Google has to decide that, or they have to let others hash it out. Youtube doesn't prevent you from, for example, all banding together and suing Lionsgate in a class action.
You could also try personal suits for tortuous interference with contractual relationships (Lionsgate is deliberately interfering with your relationship with Youtube). It may be viable in some states (others, definitely not).
There are plenty of options here, youtube shouldn't be deciding this stuff any more than anyone else (for example github complies with DMCA requests, and counter-notifications, despite what they think of the actual situation).