A belt drive with integrated gearbox (no derailleur) is imho the future of e-bikes, especially as they get more powerful. This is anecdotal but based on my own experience.

I have a middrive bike, fat tire 9 speeds. It has a fairly powerful cargo bike motor that puts out 130Nm. The cassette is a Shimano HG-400, most durable option I’ve been able to find. I’ve had issues with it eating the 9th gear cog, just rounding off the teeth VERY quickly. I have to ride it like driving a big truck - have to get into the lower gears and never accelerate when I’m in 9th. That plus ordering a bunch of spare 9th gear cogs from AliExpress is workable but for somebody with less biking experience, this would be a very frustrating set up, especially if what they want to do is mostly ride around on the throttle.

In comparison, I also have an eMTB, 85Nm. I can push hard on the top gear without this problem - I could break the chain overdoing it (did that once) but it can take a ton more abuse. The cassette is an SRAM XG-1275 which is without question a higher tier of component, but the point still stands, I can abuse it without it rounding the teeth.

It comes down to the amount of power the motor + me can produce, when put through components that were designed for human output on a moderate weight bike not for human + motor on a much heavier e-bike. A belt can just take more power.