Internal gear hubs are pricy but great. I’ll strongly advise against a conventional derailleur with a mid-drive motor: the derailleur needs a thinner chain which wear faster, especially with a motor that apply more torque than a normal human. Internal hubs allow to use a 1s chain or better: a belt. Then you’re good to go for a loooong time. There’s also the (super expensive) Pignon mid drive with integrated speeds, a bit like the Schlumpf’s but for e-bikes.

Pro of derailleur’s e-bikes: their price.

[waited long time to do that] - a former bike mechanist

edit: the problem with faster wear isn’t the risk to break but the decease in efficiency which will affect your motor health (heating) and batterie capacity. If you’re on a budget there’s a compromise: find your favorite gear and replace the derailleur and cassette with a single speed front and back sprockets (and chain). Beware that might not be adapted to hilly roads as GP environment.