Over a bigger dataset, the difference for me is typically about 20-25 bpm average. That said, in one of the early eMTB races I did, my HR profile was exactly the same as it would be for an XC race or a cyclocross race. It's all just a question of how much ya wanna hurt.I did a completely unscientific test not long ago. Rode up and down a big hill on my normal bike, then an e-bike. First ride had a max heart rate of 180, average 161. On the e-bike max was 160 and average 127. I don't know enough about exercise, but I'd have to ride much faster or much longer on the e-bike to get the same workout.
NB. I deliberately rode the e-bike at the same speed as my normal bike.
I understand though. I'm pretty much limited to weekends, but notice a difference if I can squeeze in a midweek ride for a couple of weeks.