Pledge is much easier to user that seccomp-bpf and is now forced in more than half of the binary distribuited in the base system.
Also, there is a big difference between having a technology and enforcing the technology: Seccomp has been included in linux for a very long time, but is ignored by most developers and not used except in specific instances (ie chrome as you pointed out)
a fundamental difference between W^X and PAX is that PAX can be disabled on a per binary based, where W^X is applied on the whole system. That more aggressive aproach has been applied first on OpenBSD and i like to believe that's that they are referring to