> The only thing significant about /64 is that’s the smallest unit for SLAAC.

...which means you can't subnet it because you have to assume SLAAC might happen since that's the only thing ipv6 requires. Ergo, an ISP only giving you a /64 means you have to nat if you want subnets, and if you have to nat why wouldn't you use ipv4 instead where it's so much simpler?

Android only supports slaac.

Strangely it supports DHCPv6 as a server but not as a client.

It's not strange. It's Google's plan to push ISPs into supporting SLAAC and giving you at least /64 instead of giving you a single /128 address.

It is not a bad thing actually.