I can chime in, as I have both, although I currently have the KSL listed for sale.
First point is the motor and battery. The difference in torque is massive when comparing turbo vs turbo. Trail on the Levo feels a bit more powerful than turbo on the KSL, and the Levo's eco feels a bit more powerful than the KSL's trail. Realistically, turbo and trail on the KSL are both huge when you're coming off a regular bike, and it's enough for me to get up anything, to the point where traction is the main concern, but then turbo on the Levo is just truly bonkers. I did an accidental burnout on my garage floor when I was first testing it out.
The battery capacity is really the big one for me. I like being able to do at least 6k rides on the weekends, and with the KSL, you have to dial the power down so much, it just feels like a fast XC bike. I've even done a 50mi/10k ft ride on the KSL, which took me over 6 hours with battery to spare (with range extender), but I was just moving along at analog pace (9.2mph avg). I just bought the Levo a couple weeks ago, because I want to do big rides at ebike speed, and the 700Wh battery lets me do that. As a bonus, I don't have the range extender taking up my bottle cage. Here's my range table for the KSL - I don't have enough data on the Levo yet:
View attachment 105143
Regarding handling, throw the idea of weight out the door. I don't notice the difference in weight at all, but what I do notice is the handling that comes from geo and suspension setup. The KSL descends like an Enduro, and the Levo descends like a Stumpy Evo. KSL is much more planted and point-and-shoot, whereas the Levo is much more snappy and laser-precise. On capability, put it this way - if you can't ride it on the Levo/Stumpy Evo, you won't be able to ride it on the KSL/Enduro. IMO, the bigger bike just makes the ride more comfy with more margin for error, but not necessarily the difference in being able to or not being able to ride a certain feature, especially given the geo adjustments on the Levo.
If the KSL had a full-sized motor and battery, I'd have a tough time choosing between it and the Levo, but for me, the Levo is hands down the obvious choice for me, with how I like to use it. FWIW, I have a couple other buddies who've owned both, but quickly ditched their KSL's for Levos as well - and we're all young, fit guys. It's not about doing less work with the bigger motor/battery, it's about going faster. The speed is really addicting. I also find that I'm typically a little faster downhill on a slightly smaller, stiffer bike (suspension-wise), as it pumps and carries speed better than a big squishy bike.
Here's a couple clips from some filming I did on the Levo yesterday - As you can see, it turns very well!