I agree android is deffo flaky on ipv6.
Older android if you disable radvd (whilst keeping dhcpv6 enabled) would prevent them from using ipv6 with rest of your lan enabled, not so sure about latest android.
However I noticed when I configured vlans on my network the ipv6 on the 2nd vlan, was making my android loop the wifi on and off. No such issues on windows machines, so that vlan at the moment is single stacked.
The xbox one situation is clearly stupid, did you report it?
PS4 doesnt even support ipv6 yet, sony in the stone ages.
I do agree tho there is some oversights with ipv6. There has been assumptions made about things like NAT (assumptions its only purpose was to port forward for lack of ipv4), and as a result features are missing on ipv6 that would be useful. Although this isnt necessarily a ipv6 spec problem but rather how it gets implemented in software e.g. the lack of NAT support for it on pfsense and lack of static DUID on xbox one.