OP seems to want to route /64 or larger to each customer, but can only have 3000 total entries larger than /128 in the expensive routers his firm owns.
Essentially the hardware doesn't support scaling a /64 or /56 to each customer, leaving OP in a terrible position when it comes to proper IPv6 deployment.
When you look at Ziply Fiber, they seem to be ripping out these types of Enterprise grade routers left and right in favor of a simple Linux box doing routing. I think a large portion of why they're doing this is due to limitations like what OP is experiencing
Essentially the hardware doesn't support scaling a /64 or /56 to each customer, leaving OP in a terrible position when it comes to proper IPv6 deployment.
When you look at Ziply Fiber, they seem to be ripping out these types of Enterprise grade routers left and right in favor of a simple Linux box doing routing. I think a large portion of why they're doing this is due to limitations like what OP is experiencing