Am I reading this wrong?
Example image, see helms.
My guess is that the i370 version has traits that cannot yet be unlocked with your current Azerite level, but the i355 version does, resulting in a higher net performance gain.
See here about the artifact level required for azerite pieces by source/slot
That post seems pretty incomplete to me or out of date… if you look at any item our site, it should have the latest known unlock requirements. They are kind of all over the place… and pretty inconsistent from certain sources.