Have you reported these performance regressions on their bug tracker?[1] I can't find it. Just time for the kernel to boot or you measuring something else?
In my experience, they have been quite responsive to quality reports. Like Mozilla, they have many tools to assist QA.[2]
Initially, it seemed to be a temporary regression. Later that it may be related to Meltdown/Spectre mitigations. Currently, it is well-known to developers and remains patiently waiting for improvement.
https://bugs.chromium.org/p/chromium/issues/detail?id=827497...