I'd argue that he has brought his own flavor to the show. He's put a major emphasis on edutainment historicals (there's even elements of this to his own Spyfall), and has knocked all of them (Rosa, Demons of the Punjab, The Witchfinders, Nikola Telsa's Night of Terror) out of the park so far. I'm sure The Haunting of Villa Diodati will be a season highlight as well. And, yes, this season is way more hit-and-miss than Series 11 going by the fan reactions and critic reviews for Orphan 55, Praxeus and Can You Hear Me?, but he's not only been bringing in classic monsters. A major complaint about Series 11 up until Resolution. He's also bringing in a fuck ton of deep cut lore from the expanded universe, both in his own scripts and those by others, as well. Can You Hear Me? might not have been "good", but it mainstreamed ideas from the novels, comics and audios about the Eternals and The Celestial Toymaker in a way that would make Moffat jealous. The real question is whether the two-part finale sticks the landing or faceplants. If it succeeds, I think many will (eventually) forgive a 10 episode series with three shit episodes that manages to pull off a Lost Doctor myth arc. If it fails, then I think Series 12 will be looked at as a misfire with a few bright spots. Mind you, this is all coming from a guy that liked Series 11 and about half the episodes so far of Series 12. Moffat4Life, though. Deadline, The Hollywood Reporter and Variety have all reported that the recent deals with China and HBO Max have helped to secure funding through Series 15. And Series 13 (with Chibs and Jodie both confirmed to return) has already been officially announced. I know that the ratings have been way down this year, both from last year's highs and also the Davies & Moffat eras outside of Series 9 & 10 (You slept on an incredible run of episodes, people!). But we're still getting three more series, which would get us through at least 2023. Honestly, worst case scenario, a big 60th Anniversary Special blowout wouldn't be a bad way to wrap up this incarnation of TV-based Doctor Who. I'm still hoping that the Beeb gives it at least one more era (whether Chibs completes his five year plan or not) to try and get the ratings turned around. This show is uniquely designed for infinite soft reboots. Exploit the shit out of that before you (hopefully) temporarily call it quits.
When Chibnall leaves, I hope that the BBC makes another run at getting Toby Whithouse for the showrunner job. Then we can finally get a follow-up on that "Minister of War" thing that got mentioned in a throw-away line in "Before the Flood."