Looking at my gpx file from when I rode it; total of 14km of DC - two short sections around Port Talbot, the Baglan bit, and the run to Swansea from there.
That seems like quite a lot to me; I understand why it's needed, though. Sometimes, to get from A to B you really can't afford to go via C.
The bit that caught one rider out was at Port Talbot, at about 47km. The routesheet just says (said) to follow the A48 for N km. This is the kind of routesheet that annoyed people on the Manningtree 400 who ended up in Cambridge about 7 miles off route, because to stay on the A48 or whatever road, you sometimes have to apparently turn off it.
This is the junction (streeview):
Google MapsIf you look at the sign you have to turn left off the roundabout then hang a right to stay on the A48.
This is what you see as you leave the roundabout:
Google MapsIt's not actually very obvious that the road you want is that bit going under the viaduct. It's not signposted at all, and it's much closer to the junction than you'd assume even if you'd noticed the A48 on the previous sign.
I almost got caught out first time on the Gower Getter. I'd done GPS waypoints for all turns, but I had that one as E2 A48 as I couldn't tell from the OS map that it was a fork rather than a separate instruction.
However, it's not at all relevant if the route is reversed, though it might be on the Gower Getter.