In the game it is basically a critical hit and there are many cases in which a hit did something like disable the radar which lead to victory. Ship duels are pretty luck based since a good hit that take out something like fire Control or radar or even worse case what happened to the Hood could pretty much instantly win the engagment.
Design issues are probably not easy to spot and may only be clear after an engagment, I suspect you would find alot of issues with the British and american ships as well but they did have the advantage of being part of a large navy and thus the fault of single ships are not as decisive. However for example the sinking of Prince of Wales did show pretty major issues with the British AA which stopped to work leading to the loss of a battleship and a battlecruiser.
With PoW, there was more than a few things gone wrong, firstly Phillips did not request the Radar be fixed when he arrived in port, despite knowing it was out of order, only asking 2 days before he sailed and the maintenance crews told him it would be 5 days of work, and the AA ammunition had degraded somewhat due to the tropical heat, and Philips, for some reason we can only speculate about, did not radio Singapore for assistance once the attack started.
Still the AA system on PoW didn't partly cease functioning until the one solitary torpedo to find it's target hit the propeller shaft and tore it loose at which point the follow on damage, torn armour plates and severe flooding, disabled parts of the ships electrical systems by flooding one of the dynamo rooms, added to this the ship developed a severe list leaving the those guns still functional unable to depress low enough to target the incoming planes.
Before that the PoW's QF 5.25" guns had actually been causing a serious problem for the Japanese bombers, badly damaging several of the high altitude bombers forcing them to disengage and shooting down one and damaging several more of the first wave of incoming torpedo bombers. Without the PoW AA fire the Japanese were able to press closer on the attack.
By comparison Repulse, which had what we might term a lower tier of protection, comparatively did not have as much success, whilst she did also knock out a few bombers, and damage more, she was firing for a considerably longer period of time, long enough that some of the guns began to jam from heat and the cordite residue choking the mechanisms.
It's hard to speculate exactly what might have happened if the PoW had a fully functional Radar controller before the attack started, and less suspect ammunition, I suspect a lot more Japanese casualties, but also as the attackers were genuinely brave and extremely determined, (in fact how they finally took down Repulse was near suicidal bravery with a co-ordinated low level attack from both sides with multiple aircraft guaranteeing they would suffer some losses), I think both ships would still have been lost.
There just would have been more brave men lost for Lt. Eki to memorialize when he flew over the wrecks the next day to drop his wreaths.