Canon do have more options in that area but the difference is not so big when you factor in things like the cost of the 70-300 DO and L versions they are really a different price.
For a budget 300mm f4 you can get the older 300mm f4.0 AF, which is also around 400 quid. Nikon do need to update their 300mm f4, it is overdue, it has been rumored to be replaced for a long time and that might happen this year.
You included things like the crop 55-250 canon, in which case you can add lenses like the 55-200 VR and non VR, 55-300VR, 18-200, 18-300, 28-300VR full frame lens.
Nikon now have a 70-200f 4.
400mm 5.6 is easily achieved with the 300mm f4.0
Nikon don't offer non VR of their lenses but I don't see this as a weakness,if you want a non-VR lens then just buy the older generation second handoff less money. Lenses like the 70-200f4 non-is are not really that important, if you want a slower and lighter lens then you will definitely want the IS, and the difference with the 70-300 IS is then small.
So in reality there is small difference. Nikon really need to get out the 300mm f4 VR and 80-400 replacements. I don't think there is a need for much else. Other areas should be a priority.