As far as the sport time, with an e-bike you only have the two options, e-bike ride or e-mountain bike ride.  Generally, I would go with e-mountain bike ride for anything off the pavement.  You can't mark it as a gravel ride since that is not for e-bikes.  Which of the two other options you use is really up to you so go with what fits the specific ride the best.

Thanks for the reply.  You've highlighted the problem I brought up.  Just how would someone know that "gravel ride since that is not for e-bikes" in the mind of Strava??  I ride major gravel events on an e-bike.  I understand and accept that e-bikes don't count for podium positions against pure pedal power.  However, the sport is still gravel riding.  I feel that, as e-bikes are the fastest-growing segment in the industry, that Strava (and the community) need to find a better acceptance of the trend.

Seems like it would be fairly obvious for someone to know that "gravel ride" does not include e-bike based on the fact that all other e-bike categories are clearly marked with "e-bike" in their name.  I agree that Strava should probably break out more divisions of e-biking with the popularity increasing like it is.

I certainly understand than a person can’t compare statistics between an ebike and a pedal only bike…. Neither can you compare a single-speed cruiser with a carbon fiber road bike. Yet all can be utilized in the sport of gravel riding. 
For the purpose of metrics, e-bikes need to be differentiated from each other.  By Strava doing so by identifying e-bikes as a sport just points to poor database design. They would be. They would be better