The front derailleur tirewidth is a standard, so manufacturers don't have to adjust the very sensitive chainstay length. Tire width is limited.I don’t see how the front derailleur would limit tire size. Prior discussions seemed to think the single chainring was a result of the large Q-Factor. Adding a second chainring would create problems in the chain alignment.
At least in the Comp line both the road and EVO models use the GRX groupset. It may have been designed for gravel bikes but it works extremely well on the road model.
I’m not sure I understand your last statement. Are you saying Specialized is marketing the Creo as a constant 28 mph bike? Being that both Class 1 and Class 3 Ebikes are pedal assist, their speed is totally dependent on the riders effort. The Class 2 Ebikes with their throttles can maintain any speed, up to their designed motor cutout, with no rider effort. I expect an extremely fit rider can maintain 28 mph fairly easily on a Creo while the rest of us mortals only hit that speed occasionally.
The Q factor width is also a standard, from Shimano.
The manufacturer chainring plays a role, too. You'll notice Praxis chainring and cranks, not Shimano. It's very detailed.
No, I am saying that designers make tradeoffs. They favor certain benefits and costs. For example, a small change like a few mm increase in tire width causes a 4% decrease in drivetrain efficiency. We can feel four percent extra pedal force, but we cannot visualize it.