Sounds like you want the smallest motor possible. A strong biker does 250 watts, so a small 250 watt motor will give you plenty of power in bike terms. The smaller the motor, the lighter the bike will be.
I like the idea of a Fazua motor as seen on something like the Canyon
https://www.canyon.com/en-gb/electri...s/endurace-on/
looks like a normal bike, rides like a normal bike, and gives you a boost if/when needed.
The downside of any European focused bike is they are limited to 25km/hr. My first ebike was built like that and I found it had near infinite range, because I don't ride that slow. ;-)
I did end up throwing a small hub motor onto a road bike. 19lb bike became 29lb bike, and rides just fine with no power assist - its still lighter/easier than most mountain bikes.