[tree_enjoyer]

A traditional bicycle chain drive is something around 98% efficient - particularly if you're using internally geared hubs or a single speed with the chain line perfectly straight. What's a typical consumer alternator efficiency? Maybe 85%? And then a few steps for losses in the charging circuit and then again at the motor.

Not even napkin math, but ballpark I would think you're looking at having to pedal about 20-25% harder to accelerate the same rate compared to a chain, with no supplemental energy directed towards charging the battery (though I would assume al the energy goes through the power management system anyways).

However you get some gain in that you don't have to select a gear ratio, and that the electric motor provides torque efficiently at any rpm you can realistically expect on a bicycle. If it has an adaptive resistance level it will probably be more work (energy) but for many non-cyclists feel much more intuitive and simple