I still don't see an issue.
You may misunderstand the purpose of those IPVx_ADDRESS settings.
The IPV4_ADDRESS and IPV6_ADDRESS variables in setupVars.conf were originally intended to control the IP address that Pi-hole should answer when configured for one of its IP or IP-NODATA-AAAA blocking modes.
Since Pi-hole FTL v5.8 (see section Automated IP blocking mode), Pi-hole dynamically determines the address to use based on the query received. Strictly speaking, the respective IPVx_ADDRESS settings have become somewhat obsolete since then.
The purpose of providing name resoluton for pi.hole is to allow access of Pi-hole's web UI via that name. That purpose is accomplished when providing an address that is accessible for a client.
It seems that does work in your case? Please elaborate if it wouldn't.
And as far as Pi-hole's DNS operation is concerned:
Interface listening behaviour is controlled by a separate set of UI settings of its own.
I agree that Pi-hole could answer the full set of IPv6 addresses associated to its host for pi.hole.
On the other hand, just providing a single address makes for a smaller size answer, and it spares your clients from selecting a suitable address from a set.