So, I went to my LBS and tried a bike with a Shimano E6000 motor and a 44t chainring fitted. It mostly alleviates the problem of low speed while muscle powered. Mostly. I could at least get up to 40km/h in a slight downhill and not be completely spun out.

Also, the sales guy at my LBS claimed that it was well known that e-bikes, especially mountain e-bikes, had this problem with a low top speed for muscle power. But I've been researching e-bikes for almost two months now before I finally bought one and I've never heard this mentioned.

As far as I can tell however, the e6000 chainring is not compatible with the e8000 motor. That is a major bummer. Anything besides returning my bike I should look into?