Luzow. 24 heavy caliber hits. total KIA 121. Indefatigable, Invincible, Queen Mary 8-11 heavy caliber hits (at least four being 28cm) combined. ~3,000 KIA.
In all three cases of the British ship being lost it's due to turret penetration and flash.
1. See my post above related to deck armor failure directly leading to the loss of two ships due to insufficent protection of magazine spaces.
But that wasn't
because of insufficient protection of magazine spaces, it was because of turret flash as far as any of our accounts of the battle can tell. In any case, deck armour failure is not belt armour failure, and the British and German BCs had comparable deck armour. (Queen Mary had 2.5 inches, Invincible had 1.5-2.5 inches, Tiger had up to 3 inches, and Derfflinger had 3.1 inches.)
Which aspect of the protection of the battlecruisers do you consider inadequate? All of it, the belt, the deck, what? (Because you've repeatedly referenced the belt armour, but so far as I can tell it's
Lutzow not any British BC which was rendered hors d'combat due to belt armour penetrations.)
2. Of course not. What was inevitable was that the lack of sufficient mechanical interlocks would be exploited by sailors in the heat of action. That is why mechanical safety interlocks needed to be introduced AFTER Jutland. They were not.
But there were mechanical safety interlocks
before Jutland, they were just wired open - and
after Jutland they weren't, so the ships were protected against flash. It's a shame it took the loss of multiple ships to get the point home, but if you consider sailors disabling the anti-flash protection a fault it's worth remembering that
any anti-flash protection can be disabled.
3. This question has no OTL answer because the RN, Admiral Fischer in particular, became overly enamored of the BC concept. This being the case not serious effort was put into a heavily armored, fast vessel (call it an evolution of the armored cruiser, or an overbuilt light cruiser, or, as it eventually became known IOTL, a heavy cruiser) that could deal with destroyers or pure scout cruiser and outrun an enemy BC. 1/3 the cost, 1/2 or less the crew, 30+ knots with either 3x2 eight inch or 2x2 9". Not going to be able to trade with a BC (of course the RN BC were less than ideal for this task).
But that's going to be easily fended off or destroyed by the German BCs, unless it's got far heavier armour than the actual RN BCs did - and I'm not at all sure that such a heavy cruiser is really possible at the time. (The time being the decade before Jutland.)
Comparing
Hawkins (the prototypical CA) she was LD 1916 - a decade after the first BC - and cost £1.5 million. The
Tiger cost £2.5 million and had only three fewer knots, and the
Repulse and
Renown cost £3 million while actually being faster. Your mileage may vary, of course, but the BCs of equal speed to the prototypical CA were built earlier, had far more firepower and were also much more heavily armoured.
A scout screen of
Hawkins against one of
Renowns would be, I think, a clear decision for the faster, better armed, more heavily armoured ships of twice the cost and 30% more crew. (
Hawkins crew 712 normal,
Repulse crew 919 normal.)
The BC concept, as executed IRL was a disaster. It relied on the enemy not reacting with ships of equal if not better quality allowing the BC happily reap armored cruisers while chasing light cruisers and destroyers out of range of their heavy guns.
From all accounts Fisher considered it sufficient to
force the enemy to react with ships of equal quality, out of less total resources. (For the price of a given BC the German navy could have had two DNs, comparing the
Derfflinger and
Konig classes - if the Germans
hadn't reacted to the BC class they'd have had a battle-line something like eight to ten ships stronger.)
The real error was pursuing the concept once the expected OPFOR matched them, this was compounded by believing they were suitable to engage with ships with equal and superior protection in a task that was far better suited for a less expensive faster and more survivable ship type.
At any given time the OPFOR's battlecruisers did not necessarily match the British BCs - the
Renown and
Repulse missed Jutland by bare months and are significantly superior to the
Derfflinger class.