My fairly lightweight ebike (70 lbs) designed to hit 28 mph is running at right around 2000 watts right now.
Actually I fiddle around with the precise amount to make it "just enough" so I can climb the very steep roads in my area which hit about 10% grade.
At 3000 watts I could do all the hills and not pedal. At 2000 watts I need to pedal very hard or the motor stalls.
Below 1500 watts and my legs and the ebike just won't make the hill.
My area has some rather extreme hills and I know that most roads are built to a limit of 6% grade.
If you were in Europe and lived in an area of extremely steep roads (which they did a lot back in older times) you would need that level of power UNLESS you went to a mid drive and ran the power through multiple gears.
But then you have the maintenance problems with rapid chain wear.
A very low powered 250 watt mid drive could get you up anything if geared down to a crawl.