Which e-bikes have you been looking at? I've ridden the Trek Powerfly and the YT Decoy and they're both exactly like what you're looking for. They only add to your output and in proportion to it. I also have a Raleigh cruiser e-bike and it works the same way. I was under the impression that all but the cheapest class 1 bikes work the same. I have ridden a couple rear hub drive bikes like the Rad Rover and they have a more "on or off" feel. The motor starts as soon as you start pedalling at whatever power setting you have selected

Thanks for your comment! I have tried the Rad Bikes and I had the exact same feeling like you. No cadence assist for me.

I looked at all the bikes you have suggested, and sadly none fit the bill. I didn't think they would - I have studied the subject extensively.

1. All popular mid-drive motors such as Bosch and Shimano are designed for European market, capped 250 watts, sometimes 350 watts. The max legal in the US is 750 watts, and I really want the max. I might even need the max when bike packing, or simply climbing up the hill where I live (it's pretty bad).

2. All legal powerful motors are rear-hub or front-hub. They can't take advantage of the rear wheel gearing, so they can't climb the hills. Rad Bikes have it written in the instructions that one must not use max assist when climbing uphill.

3. One can find non-street legal motors (how about 3000 watt) and they will climb rather well without gearing, but I want to stay within the law and conserve battery power. They are also heavy, and I might need to carry my bike on stairs.

4. There is a handful of street-legal powerful mid-drive motors, but they are mostly use on custom builds (Bafang, Tonsheng, etc), and even then only some of them seem to support torque sensors.

Then there are other concerns: it's nearly impossible to find full-size folding mountain bike, they are all 20" tire size. The $4k+ tag is about twice as much as I am planning to spend. Most of the bikes have rear shocks (stealing power - see "bike bobbing").