I may not know a lot about e-bikes, but it's regular bike components that I
do know about. Most of my experience modifying drivetrains has to do with recumbent tricycles (which I'd recommend if your budget allows and you can meet spatial requirements for storage). Drivetrain principles should be similar as they share all the same components.
So you only have a single chain ring. That's pretty big for a single chain ring setup. 52T is huge and is often times bigger than most people's largest ring who have a 3-ring setup. 22-32-42 is a common 3-ring setup for mountain bikes. You can imagine the design was made to help go up hills in less-than-perfect terrain. If you plan to stick with a single chainring setup, then you'll have to find some sort of middle ground. I'd try a 42 chain ring and see how that works for you. Ebikestop has some cheap ones you can try. Make sure you get the right type that will fit the number and spacing of the bolts you currently have. Your manufacturer should be able to tell you if you don't know or can't measure.
You'll see a difference immediately with the swap. Note this will limit your speed on downhills and flats. That's the sacrifice. For further ability to go up hills, I use a 11-34T freewheel (in your case, probably a cassette). Going from the 14T to 11T will help compensate a bit for the loss from going from a 52T chain ring to a 42T somewhat. The 34T cog will help you tons compared to your stock 28T cog on your existing cassette. For pics and details, you can visit my e-bike blog in my sig or head over to my bent trike blog: kmxtornado.blogspot.com
Good luck.
The basic thing is: The bigger the chain ring, the more difficult it is to go up hills. The opposite is true for the rear cassette. The larger the rear cogs on your rear cassette, the easier it is to take on those hills.
ANOTHER CONTROVERSIAL THEORY WORTH THINKING ABOUT:
Those at the recumbent forums at bentrideronline have noticed that reducing the length of your crankarms from a typical 170mm or 175mm length to something like 155mm helps a lot. Much of this choice was a response to experiencing pain in the knees. It's more noticeable and necessary for recumbents due to the physics of the angle at which we pedal. We can't use our body weight to pedal like you roadies can. I can see a benefit for your application too though b/c it will require your knees to bend less with this setup.
The crankarm is technically a leverarm in physics terms. If you shorten it, technically it's suppose to make it more difficult to climb hills (same theory as why chain cutters have long handles for leverage). For at least us bent guys, most of us find the opposite is true. Although we lose physical leverage, but b/c we don't have to pull our knees up so high and the degree of movement is less, we're able to spin and climb hills much more efficiently and more comfortably. Timing and gear changing is more important for bent rides than DFers, so it should be easier for you as an upright cyclist.
Again, this is not the same for upright DF (diamond frame) bicycles, but similar. It might be worth trying a shorter pair of crankarms to see if it works out for you. Start with a cheap set in case you don't noticed any improvement you won't be set back so much $$$.
What you're looking at above is a 170mm crankarm at the top followed by another of the same size. The third one down is a 155mm and the last one at the bottom is a 152mm. For my application, 152mm was actually too short. I prefer 155mm but it will depend on each rider. Just wanted to note that it is possible to go to short. And remember, reducing the length on the crankarm by whatever mm is multiplied by two in use since the difference in length applies to both arms.
