I am not on the Chrome architecture team, so I cannot predict with certainty what they would choose to do, but I can at least provide my opinion and hope that it doesn't stray too far from what they think ;)

As for an overall summary, I think it is accurate to say that the OpenBSD people are obviously not idiots, and that they do make a lot of right choices. However, those decisions are (as I have mentioned elsewhere: https://news.ycombinator.com/item?id=26911420) mixed with some questionable ones. Overall I think they do adopt a lot of the right things–the ones you mentioned–and I do agree that they are fairly quick to do so, although sometimes they seem like they want to claim a bit more credit about being "first" or designing something than they really should. But those are social issues, so it's not really worth talking about them here.

My main issue is that some of the OpenBSD mitigations seem to be designed by people who either have an outdated view of how modern exploits work, or are just entirely wrong. Like, they sound plausible for a bit if you just think about them, but if you look at real exploits you realize that they are not worth it, or they are just not how real chains look like. Ok, let's break this apart a bit.

What does it mean to have an outdated view of exploits? This means that you're protecting against things that nobody does these days, because other mitigations exist to prevent it. If your mitigation protects against something that people used to do when NX didn't exist and ASLR was nonexistent or weak (perhaps due to lack of VA space), then it's clear that you're living in the past. Similarly, if your mitigation is intended to protect against some form of attack, but if these kinds of attacks never actually happen in the wild, or protecting against them opens up an alternative vector that you leave open, then your model is incomplete. Finally, when judging a mitigation, you don't look at what fraction of some exploit it mitigates when it is working perfectly–you need to consider it in the context of other things failing. ASLR is a "weak" mitigation because one partial, mildly controlled read might be enough to break it. Privdrop is a "strong" mitigation because there it requires a full kernel chain to undo. That doesn't mean they aren't both good to have, but it is important to keep this in mind when evaluating this kind of stuff. Anyways, onto some of the worse mitigations.

Syscall origin verification seems like a weak hardening technique, designed with a lack of understanding of what kind of attacker might exploit it. The reasoning seems to be to prevent an attacker from doing things like writing a syscall into a JIT region, but generally attackers at that point can easily craft shellcode that gives them arbitrary R/W (or have this already), which lets them jump through libc anyways. As such, the general understanding is that it is pretty much useless at stopping an attacker at the level of control it claims it can protect against.

ROP gadget removal is similarly problematic, because "removal" in this case doesn't mean "full removal", it means "reduction in their frequency". A ROP chain doesn't actually take that many gadgets, though, so you can do things like remove half or even more of all gadgets with pretty much zero impact on the ability to ROP. (And I'm not even going to get into the fact that using dumb gadget finding scripts, like OpenBSD did, is not how you measure gadget reduction.) And even once you have all the ROP opportunities removed, you need to then start looking at JOP, because that's what attackers are going to pivot to (heh), which AFAIK is not yet being considered.

I'll do one more, but hopefully you get the idea by now: trapsleds are basically considered to be a joke. They are meant to protect against ROP nop sleds, except it fails to understand that these don't exist. When people ROP they jump precisely to where they want to go. It sounds good on paper, but in reality the mitigation just doesn't match up with any real attacks.

There's a lot of good going on in OpenBSD, but there is also some places where they seem to not have caught up with what is going on in the real world. And I think people's general criticism towards the mitigations follow along those lines.