Correct me if wrong but the firewall is not aware whether a particular (VPN) route is up/down and it requires a script or deamon to monitor the connection state and take action (kill switch via script) when the route is down. Common scenario with split routing where some clients are routed trough the ISP’s WAN and some through the VPN.
OpenVPN was brought in as comparision of not being curtailed and having such up/down script snippets too. Yes, the basic implemention is different but the functionality of shell script snippets is similar.
I am not sure whether you made the effort to read into wg-quick and the abilities. It is greatly enhancing the basic wireguard.sh and not shell hooking but making similar system calls, e.g. you can
PreUp = ip route add x.x.x.x./x via x.x.x.x.
PreUp = iptables -A …
PostUp = ip link add dev …
PostDown = systemctl -w net.ipv6.conf.all.disable_ipv6 = 1
No weird hooks, just common shell script calls to the system environment.
Whether I like it is beside the point, just what are you arguing resonates as not certain whether you actually looked into wg-quick. As you are however open to it I would hope that you do.