Saw your post over on that other project's forum. PPPoE multi-WAN with the same gateway IP has worked in pfSense for quite some time, that only works in OPNsense because we fixed it years back (the only thing they've actually accomplished functionality-wise is breaking things that worked in the code they forked). I'm guessing you found some really old references that are no longer applicable. Maybe you have an unusual edge case, which if that's the case, please start a new thread describing what you're doing. Multiple PPPoE with the same gateway most definitely works though.
With pfSense, when you boot up, your rules are actually loaded correctly, unlike some other projects. And our reply-to actually functions, unlike some others (that bug should really be labeled as "multi-WAN is non-functional for all inbound traffic"). Multi-WAN IPsec works, unlike some others. I could go on. Suffice it to say, you're in for a world of hurt if you continue down that path. They've broken a lot of key multi-WAN things where you won't have those issues here.