I had exactly the same damage on the rear wheel of my Stromer speed ebike in the rear wheel after 15 month. Surely there damage was there some month and km before, but I noticed it for the first time after 14-15 months.
We have quite strong laws for warranty here up to two years. But as I had almost 10.000km on bike and wheel, they first wanted to charge me for the new rim. As Stromer ebikes are for commuting and 7000km per year quite normal, I protestet and finally they paid all.
On the other hand I had a defect Nuvinci/Envilo rear hub on a Riese&Müller ebike after 4 years and dealer and producer rejected a warranty case. Also this was not ok, as the problem appeared for the first time after one year. But dealer and I first thought we can fix it somehow and missed to instist on a warranty replacement. But my protest here was without luck, they made me a "special offer" for a new rear wheel for $450 instead of $600. What still was an impudence as you could buy similiar rear wheels online from any dealer for $300.
So if your damage/wheel is in the first year and maybe below 5000km, dealer/producer should pay it. And if not, $400 for a simple wheel without any special parts is as well an impudence, you can get adequate wheels for $200. Also it's possible to change just the rim (that happend on my Stromer and until today with another 10.000km without any problems), what should cost $100-150 for rim and work.