Haven't been into mountain biking components for a while now, so what I am saying might be wrong, but deore used to be the rank below SLX, it went something like Deore -> SLX -> XT -> XTR, if it doesn't have the shadow+ (it might just be shadow without the plus aka the lever) one can make the argument it isn't an actual upgrade from a practical perspective, if it was the XT model without shadow+ instead of the SLX with shadow+ maybe it could be considered a definite upgrade since the XT had better pulleys.
Shimano Parts â–¶ New DEORE M6000 has a capable wide gear ratio that delivers a smoother gear step in all riding conditions. â–¶ Model: black
www.bike24.com
Shimano SLX RD-M670-SGS Shadow Rear Derailleur long 10-speed
www.bike24.com
At least a few years ago the difference between the Deore and the SLX on the rear derailleur was weight, which didn't matter much back then, and it sure doesn't matter in a ebike, personally I would prefer a deore with shadow+ than SLX without it, but from a purely price perspective they have definitely upgraded it or at least sidegraded it.
EDITED: Oh yeah obviously if it ends up being the SLX with the shadow+ which it doesn't look to be by the photo, it would be a straight up upgrade.
Had no idea about that, thanks for the information, it is most definitely something I will look at when my bike arrives.