I am sorry, but does it really matter what wallpapers are included with Solus, when you can choose any wallpaper you like ?
You can right click any picture you want, and choose "Set as Wallpaper".
This is a nice site to get wallpapers: https://www.opendesktop.org/browse/cat/298/
Another nice site: https://interfacelift.com/wallpaper/downloads/date/any
antechdesigns have shared a lot of wallpapers here: viewtopic.php?f=22&t=9184
Others have shared wallpapers here: viewforum.php?f=22
You are free to do whatever you want, knock yourself out.