Did you watch that video? The solar panels are not even able to fully handle their appliances and AC, and they still use a generator to supplement. They aren't used for charging a car battery at all.
>but this discussion is about what happens if you optimize the vehicle for solar at the design phase
It still doesn't change the equation because you're not looking at a order of magnitude difference. In the case of RVs and the YouTube videos you posted, you don't need to worry about what happens if you 'optimize' a vehicle for solar during a design phase - just do a back-of-the-napkin calculation by doubling the output and ... nothing changes. The challenges are the same. The use-cases are still the same (namely, hope for sunny days to generate power to run some appliances). You're still not making any meaningful progress towards extending EV range - and that's assuming double output (and you're not going to get double in the real world).