I don't think this is an accurate description of the responsibility hierarchy. If in fact the code by Netgate or associates/ contractors/ employees of Netgate is not of professional quality, it has no place in the FreeBSD codebase ready for a stable release. Ultimately, the FreeBSD core community/ developers are together responsible for the codebase even if you cannot hold them legally accountable because of the license. They together hand out and take back (deny) the commit rights (bit, whatever). If a highly sought after component _in the kernel_ is (at least to Jason's account) not even up to the lowest security and code quality standard it has no place in the code base in preparation for a stable or probably even a beta release. Other developers (and that's where Jason is completely in the right if his account is correct) should protest the inclusion of such possibly very bad code into the codebase more or less in late preparations for a release as I understand it.
So it is first and foremost on Netgate, if Jason is right but right after that it is on the other responsible FreeBSD co-developers. I mean having so obviously bad code in any kernel of a modern operating system release would be really, really bad. There are many people and companies dependent on it that cannot really influence anything but have to endure the consequences either way. I mean, if you buy a storage appliance, a router or a firewall you trust the quality of the product to a degree and cannot really audit much even if you had the skill. You have to take the word for it and make some reasonable accomodations. No insurance is going the replace the full damage due to lost data to an attacker or a bug. Peoples lives sometimes indirectly depend on the full chain of competence and no insurance can resurrect the dead or right the good name of anybody. Remember, most of the time when you have to update anything for security reasons, somebody didn't understand the system fully or just plain messed up. The only exception is when the problem or times / requirements have changed (e.g. the computers got so fast, we have to transition to longer keys/ passwords whatever).
So yeah, if Jason's account is accurate it is bad the code landed in the codebase at all and raises questions about the quality and security of FreeBSD. I mean, it is code directly meant for a secure-as-possible VPN and something that often directly interacts with the open internet. Surely such code should experience extra scrutiny.
From the short personal interaction with Jason he came across as quite thoughtful and knowledgeable. Over the years, he and his supporters were able to convince many not so easy to convince people about the quality of Wireguard and some of its implementations. He and the supporters have shown a long term commitment and I am for these reasons inclined to trust Jason's judgement as well.