As I understood it...the KGV class was largely hindered by the fact that the Royal Navy was actually building the ships according to the naval treaties enforced after World War I. If I remember correctly the KGV was not finished within the bounds of the treaty (because by the time they were ready everyone else had already broken it) but it was furthest along in initial design and did try to conform originally. Maybe you can comment in a more meaningful fashion 
I have heard some argue that, given the restrictions, the KGV is probably the best design possible given the treaty restrictions.
IIRC The restrictions were loosened by 1935, from 35 to 45,000 tons. IIRC 1935 was when when the Brits began design of the
KGV. Technically
KGV was able to have heavier armour because the now slightly-less lax restrictions.
In a fair fight, the
KGV was at least fairly equal to the
Bismarck-class. Sure it's 14in shells weren't as rawly(New word apparently) powerful as
Bismarck's 15inchers, but it was pretty vulnerable to plunging fire, at best.
To expand a bit more on my point about Brit ships being a bit underrated,
HMS Repulse was said to be a crack-gunnery ship(IIRC she wasn't deployed to follow the
Bismarck because of her thin armour. The
Renown-class Battlecruisers, IIRC weighed something about 26,000 tons.)
HMS Hood would up blowing due to a freak hit. Hell, I don't think we really know for sure
what took her down, ranging from
Bismarck just hitting at the right moment, to one of
Prinz Eugen's 8in shells punching through the deck armour. Hell, I even heard that Bismarck somehow hit 2 out of 4 shells and one went through the deck armour.
It's odd, at best. (Somebody suggested to me what would of happened if for some reason
USS Iowa took the
Bismarck's place...)