It's not as if he doesn't acknowledge Gausman in there.
"Gausman leads in FIP (2.17) and WAR (5.2), but his 3.12 ERA and 3.44 xERA, to these eyes, make him less likely to get serious traction against this competition."
That's not unreasonable. We know Gausman has had great peripherals, but has gotten both a bit unlucky and hit hard when guys do make contact.
His statcast numbers have him as elite at getting guys to chase and at not walking guys. But those same numbers also indicate when they do hit him they're barreling him up and hitting it fairly hard. Between his FIP and his xERA, it's not really unreasonable to split the difference there.
There's more numbers than just WAR now. Gausman has been pretty elite, but by xERA he's been worse than the four pitchers the writer listed. If the writers placing more weight on that particular number than it seems fine.
Every year that goes by we get a little more data allowing us to get even more granular when evaluating players performances. FIP was what it was about a few years, and now there's even more stuff.
Which is why there's both a completely reasonable case to say Gausman has been the best pitcher and to say no he's been great but not one of the top four guys.