If you're going through all that effort, then why bothering with hardening Chrome? Why wouldn't you start with Firefox, which doesn't require unGoogling to be considered secure?
OpenBSD's Chrome had pledge() first, but you're right, I should consider Firefox.
However, there was a recent Firefox bug in OpenBSD, and the patches weren't applied uniformly. It does seem that Chrome is more consistent, and gets more attention.
This is my experience in removing the ARC firmware code from two different HP desktops (I attached both BIOS images):
https://github.com/corna/me_cleaner/issues/233
These PCs are quite inexpensive. I run OpenBSD with hardened Chrome on one of them, for all of my finances.