The idea of using git as a blob storage and building entire new machinery on top is definitely a worthy one. At this point though, the de-facto baseline is no doubt git. If git as a store withstands the abuse of jj and jj becomes the industry standard, then I would agree with you. Also, at that point they may drop git backend entirely just because of price/performance discrepancy. git is overweight for what it does, if they make it do only the bottom 20%, then things will get funny.

Still, many oddities of git are inevitable due to its underlying storage model, so it makes sense to explore other models too.