"Full Fat Full Fun" all the way.
I've got a Bosch CX and it literally eats the steepest hill I can find near me.
Strava claims it's 13% Gradient but I think it's more than that
Actually I'll add some street view pics of it.

That's a pretty steep hill right? on my old 12kg bike I would manage about 30% of the way up then decide to just push my bike up...
On my new Bosch CX 27kg EMTB I literally can fly up it at 14mph, It's still a bit of a workout but I could probably go up and down it a bunch of times fine enough.
Lets face it on a light EMTB your not gaining muscle from these hills unless you ride them all day, same thing on a normal bike imo.
Get a full fat, do squats if you want thick legs., it's more fun and less pain.
Light EMTB no thanks... half fat roadbike maybe, I'd still prefer a full fat and a 700watt battery though
On mine with a Bosch CX and 750watt battery tour+ mode lets me do around 40-50 miles off offroad trails.
proper MTB courses with a lot of climbing to the trail start won't get you that distance but you would measure the battery life in altitude climbed.
seems like your more likely to be just offroad trailing which is what I do most of the time.
IMO Full fat and don't look back.