I think to guess the team pecking order we have to guess the engine/PU pecking order first:
Mercedes
RB-Ford, Honda
Ferrari
Audi
Since Mercedes became a supplier in the 90s, their engines have always been at or near the top of the field; I expect no different. Red Bull I have reliability questions over more than performance, as a new 'OEM' and whatnot, even if there is a lot of staff poached from Mercedes HPP. Honda might not have the peak of RB but they are now much more experienced with 1.6L V6 turbo than 2015. I doubt there will be a repeat of 2015.
Also I believe some of the Honda work is being done by HRC US which has been working on turbo V6s for 13 years in Indycar and also worked on the "shelved" 2.4L hybrid V6 Indycar project that more or less went into the Acura ARX06 prototype LMDh that runs now. Obviously not a 1:1 transfer of info but their knowledge pool is deeper than it was at the last reg change for sure.
Audi might have some Binotto trickery sprinkled in, but as a new OEM to F1 without a lot recent relevant experience I can't rate them above last in good faith. Ferrari is a total mystery box imo. Usually there are lots of "Ferrari is ahead" or "Ferrari is in shambles" "news" that, unless I completely missed something, are not materializing (yet). I don't have a lot of faith in Ferrari in general at the moment, though, so I would not be shocked to see them be slightly behind.
So, that brings us to the teams:
McLaren
Mercedes + VER + ALO
Williams + LEC
HAM + STR + HAD
Alpine
Racing Bulls
Audi
Haas
Cadillac
I separate the Ferrari, AM, and RB teammates because I think you will have at least a 0.3s gap between them which is a delta more than enough to fit one or more teams into.
I reckon the bottom 3 teams will struggle to score points and the average delta from P1 to P22 will be around 2-2.5s/lap.
Whether or not ground effect ('22-25) or flat floor (pre-'22) knowledge will be more relevant is a good point. I wonder if we are headed for another high rake vs. low rake kind of situation. I, like most, have not read the 2026 rules in detail, but I wonder what kind of trickery we could see on the floor edges and in front of the rear tires or if that has been properly guarded against in the new rules. IIRC Vowles (or some other TP) mentioned concerns over front skid wear (in relation to when the front active areo should activate to reduce front load and therefore raise ride height) which would seem to indicate a nose-down/high rake philosophy.

