> The RAM is not unusable, it will be used. Some portion of ram may be unallocatable

I think that's a meaningless distinction: if userspace can't allocate it, it is functionally wasted.

I completely agree with your second paragraph, but again, some portion of RAM obtainable with overcommit=0 will be unobtainable with overcommit=2.

Maybe a better way to say it is that a system with overcommit=2 will fail at a lower memory pressure than one with overcommit=0. Additional RAM would have to be added to the former system to successfully run the same workload. That RAM is waste.