This isn't really true is it.
This, if you stick to main A or B roads you are fine, it is also about man and machine, if you know your car its generally not an issue. Big vehicles have being roaming our roads for years, vans, trucks, 4x4's etc. The only time a bigger car that is wide is an issue is on really remote roads and normally such roads pose an issue to any car as are generally single track.
I've just gone from a Golf R to an F Type SVR, the latter is a much wider car and heavier, yes I can feel both but does it really impact my ability to get about, absolutely not, all I would say if your are a narrower road where only two normal sized cars can barely pass, then of course in the Golf I was quite happy to take such roads, in a larger vehicle I'd rather stick to a main road.
I did NC500 along with ten other Mustangs, which is a wide car and none of us had any issues at all, it was nothing short of incredible fun.