With clarity and truth, comes better discussion and solutions!!!
In this case there is no difference to anything Ive said thus far.
No need to mangle for WAN1 as its primary.
For WAN2, again no change for what Ive stated, but the only difference is the addition of a wireguard work around rule due to a bug.
For some reason the router ignores the mangling routing and return traffic for the handshake coming in on WAN2 still goes out WAN1.
Best solved by the following dst nat rule.
/ip firewall nat
add chain=dstnat action=dst-nat dst-address-type=local in-interface=WAN2 protocol=udp dst-port=wg-port to-addresses=ip.of.wan.1
Easy if you have a fixed WANIP, if not then you will probably need a script to ensure its updated when the dynamic IP changes.