It's cool to use only streaming ratings, but to go off about how shytty the show has been going viewershipwise(in your wrong assumption) when cable viewership is also at play.
Biggest premiere in Hulu history (I know "but,but it premiered 2 episodes!

") and to that I say........so?
The debut of the FX limited series "Shogun" has proven to be a hit with audiences.
variety.com
It seems this article goes directly against the narrative you trying to paint about poor streaming numbers.
How good is Shogun? Good enough to crush Netflix in back-to-back weeks on the streaming charts, something we rarely see,
www.forbes.com
Then there is this
Earlier this year, FX released a brand new limited series called “Shōgun”, which is based on James Clavell’s novel, FX’s
whatsondisneyplus.com
That is on top of the 500k or so weekly viewers it gets on cable.
That on top of the awards buzz it is getting, the renewal makes sense.