I don't care what kind of optimization magic Google will throw in there, a 2800mAh paired with a 5.7" OLED will not end well.
Most "normal" users don't uses their phones as much as we aficionados do, so should have no issues with a 2800mAh battery driving a device with a 5.7" OLED.
If you add the fact that the 4 features a 90Hz native refresh display, that would certainly make it a much greater challenge for daily use, except for one thing: you can't look at the change of two performance driving specs to the exclusion of all others in estimating results.
Big mistake to not acknowledge that the SD855, a 7nm chip, is 40% more energy efficient than the SD845, a 10nm chip, as used on Pixel 3/3XL.
I could just point to that and the battery and say "hey y'all, battery life is going to be through the roof with the Pixel 4!" but I'd be just as mistaken.
Another counterpoint to the 90Hz display draining more energy is that we have absolutely no details on the "neural core" - depending on what tasks are offloaded to it (presumably more than what was delegated to the "visual core" that it would seem to be replacing) and the relative efficiency with which it handles it, this could represent further energy. And in contrast, we don't know additional energy cost with Soli and the other new sensors.
The actual battery life will fall somewhere between the two extremes, and we'll have to wait a bit to see where.