Wayland isn’t to blame for duplicate effort. Instead of 4 different efforts doing the same thing, they can collaborate to build a common base. Heck, wlroots is exactly that.
There’s a ton of duplicated work in Linux ecosystem. Just think about every new distro coming out doing the same things other distros did. Just think about all those package managers on different distros. They do almost the same thing. Do they need to have codebases that share nothing? No. But they don’t care. They rather duplicate effort. They chose this.