The reasons for the bias are simple really. When the Kalkhoff was introduced the Gazelle was still stuck with the 8 Ah battery, which I understand is incompatible with the later 10 Ah, and it had a much dearer list price, having recently gone up. It also didn't have the high power mode.
Not only was the Kalkhoff Agutta cheaper, there was a long introductory offer which made it several hundreds cheaper, and it was a lighter bike as well, the Gazelle being heavy for what it is.
I believe the Gazelle now has the 10 Ah battery, but I don't know if it has the high power mode yet, and if they don't publicise these things, they've only themselves to blame for lack of interest.
There's also the value for money of the Gazelle's extra cost. For most owners, things like the big sticking out quick saddle adjustment device is just an expensive heavy gimmick, since the saddle is adjusted just once, when they get the bike first. Only with dual owners would it really be useful. The same applies to some of it's other features like the streamlined headlamp moulding into the forks, pretty to look at but difficult and expensive to replace after an accident.
There's no doubting the excellence of the Gazelle Easy Rider, but for practicality and value for money with slightly lower weight and similar European quality, the Kalkhoff Agattu wins easily. The fact that e-bikes don't need many gears doesn't help the 8 speed feature anyway, I lived for years e-biking with five gears in my very hilly area, and on my current six gear bikes only use three or four nearly all the time.
.