Its not a low number at all,all dynos are different,some read high some read low.
My tuned 6l with exhaust and diff gears runs 12.9 with only 317hp at the tyres,dyno readouts mean basically nothing,its a tuning tool comparing power gains when adding mods and checking afr and faultfinding,hp readout is a biproduct that can be fully doctored for wank factor,how its strapped down,tyre pressures,correction factors etc can change it greatly,different temps in different states,different types of dynos,hub dyons,wheels dynos blah blah blah.
Other 6.0 cars running my same/similar times can make between 350-380hp at the tyres,they arent making more power,the dyno says they are....
All tuned cars with the roughly the same parts make roughly the same power within a few hp,dyno readouts make it an internet talking point,it means nothing.