On the topic of radial tires:
To clarify I ride lighter e-bikes (44-49#s) and ride my e-bikes mostly on hard pack with tons of loose rocks, like endless loose rocks. Plenty of jumps, drops, ledges, etc. Not much to push against in the way of berms or solid traction.
On an e-bike for me at 180#s, Schwalbe Trail carcass radials are pretty bad actually. To the point of feeling dangerous at times, not because of a lack of traction but because you'll land from a jump and the tire will shift out of the way and you'll suddenly be on a rim and have no traction at all. You can add a lot of air, but then they just bounce and any traction improvement is long gone and they end up worse than non-radial tires. They feel like a basketball at that point.
The gravity casings though are MUCH better and I really quite like the Albert 27.5 x 2.6 gravity on the rear of my e-bike at 25psi. As in, it might just be my favorite rear tire for that application.
I don't find radials slow on trail riding at all, but that's because my trails are so rough that the radials just glide where-as other tires bounce. I actually installed an Albert trail 29 x 2.5 on the front of my trail bike, and it was great for that application. But I don't take that bike on the same terrain I take the e-bikes on. It's more hardpack and not as rocky. I did find the 2.4 Martello a notable upgrade over the Albert though, in all ways, for that application.
A couple of other notes, I personally find big tires (i.e. >2.6 actual) really gnarly to ride. They bounce and lose control easily. Even my novice 105# ex-wife made me remove some 2.6 tires from her trail bike because whatever pressure we tried, they just bounced like crazy.
Also, I own 3 sets of BERD wheels, love them in the right application, such as for my novice 105# ex-wife or my trail bike on XC tires. But I tried them on my Relay e-bike, and they were heavier duty stiffer rims, and it was actually pretty bad imo. They just move too much and don't hold the line. These are very well used wheels so I acknowledge that tightening up the spokes, or even BERD's new DH spokes, could change that entire equation. But installing CB Synthesis wheels was a revelation honestly. The CB's just hold a line much better and as such I was faster under high traction situations, which admittedly where I live, are a bit rare.
The best e-bike front tire I've tried for my very loose conditions, is the Mazza Race 2.6. Mad traction and it's held up fine for me, but I need more time on it. It likes low air pressure. I run 20 psi in it. Those Vittoria tires will be really stiff at higher pressures and feel wooden but once lowered they are similar to the Radials in the way they absorb trail chatter, yet have nice firm sidewalls.
