Have you heard of unique local addresses? Most of the LAN "problems" you describe are solved by using ULAs. Yes, even name resolution - the hosts file becomes useful again. PCP (the 2013 replacement for NAT-PMP) supports IPv6 port opening; UPnP has supported it since IGDv2 (2015). Any ISP that does not do IPv6 prefix delegation ("your ISP only gives you a single v6 address"), might as well stop claiming IPv6 support.
I am not sure why you think multihoming is a bad thing. That is one of the major things that in my experience makes IPv6 LAN configuration a lot more useful and robust than IPv4 with private addressing. It sounds like you misunderstood some basic IPv6 assumptions - configuring an IPv6 LAN is not that much more difficult than an IPv4 one. I would never go back to IPv4 for my LAN.
I am not sure why you think multihoming is a bad thing. That is one of the major things that in my experience makes IPv6 LAN configuration a lot more useful and robust than IPv4 with private addressing. It sounds like you misunderstood some basic IPv6 assumptions - configuring an IPv6 LAN is not that much more difficult than an IPv4 one. I would never go back to IPv4 for my LAN.