I'll continue my tires mumbling back here so to not pollute the Future rule changes thread. Below are two examples of cars fitted with fictional 645mm diameter, 15-inch tires and wheel so with the same tyre wall height as the 2022 cars.
So this is F: 270/645/R15 / R: 370/645/R15:
If they really wanted to go small and light than the below car is what a 2016 Mercedes would've looked like with the following specs: car on the right: F: 245/645/R15 / R: 345/645/R15 and car on the left, with the actual tire diameter of that time: F: 245/660/R13 / R: 325/660/R13 (the car on the right is 1.840mm wide at the rear because it was easier to manipulate the image with the tire becoming wider to the outside):
So 15mm smaller diameter, 20mm wider in the rear and 15 instead of 13-inch wheels. This car had a 3.500mm wheelbase (1.800mm wide), so the 2026 car would possibly be 100-200mm shorter still. To me it doesn't look as good as the wider spec on the Super Formula car above. In terms of drag and weight though, it would be really close to the pre-2017 generation tires. Frontal area is only 1% larger in total.
To me smaller diameter tires makes much more sense:
1 Lower weight
2 Less drag
3 Makes same width tires look wider/better (if in proportion to the size of the car).