Yeah, but in a car a few extra horses is a bonus.
In seriousness, there is nothing the matter with Castrol, other than being a bit expensive and they don't really make as full a range as some companies.
If you're looking at oil for a Clio, you want a 5w-40 and the Castrol Edge 5w-40 is Renault approved, but it's £45 on offer if you want 5L. You can get 5L of Shell Helix for £28 and that's Renault approved. For £45 you can get 5L of Millers CFS (£44) or Gulf Competition (£38) and they are absolute top end race quality oils, although they aren't Renault approved.
Or when it comes to things like modified Imprezas where you want a 10w-50, Castrol don't make one, you have a choice of 5w-40 or 10w-60.
Cheers
Tim