Managed to get a replacement sent out via express courier, which arrived (and was installed) on Friday. Bled it up and left it overnight with the lever tied on - with the span & ratio it was set to at the factory (I'm not sure what it is set at), I've already got much better reach and feel.
Of course, now that I can really feel the brakes, I can feel the noticeable warp in the disc
- but that can wait as the brakes are still perfectly serviceable as-is (caliper re-kit & disc/pad replacement will come "soon").
I think I've finally reached a point where the bike is more or less OK for the road, all I've got left to do is replace the tyres and the aforementioned discs/pads & caliper re-kit before I move onto customising the bike further to my own taste.