As an experienced mountain biker I’d love if the downvoters could engage with the comment. I agree with it. A proper legal e-bike, especially when clamped to 25 km/h or a similar limit, doesn’t really need that much stopping power than a comparable regular bike. Maybe the sum of all the factors (often less experienced riders, slightly more speed in some situations, slightly higher weight) warrants going to a bigger rotor diameter or a different brake pads compound, which is how it’s usually done. But it’s still nothing compared to speccing cargo bike brakes or tandem brakes, there you really have to account for the weight and go all the way to like 200mm rotors and four-pot calipers.

only real worry I'd have is a scenario like

1. someone has a cheap disc brake bike for pleasure rides (mostly in the sun)

2. they get something like this for commuting or whatever

3. now they're on their disc brake bike most days (including when it rains), going faster than they're used to

it's not the end of the world, but it also doesn't seem great

It’s directly above the wheel. I just use an ass saver and while that’s way inferior to your setup, it reduces the volume thrown up a lot.