Why does the Nelson just never do damage to anything?

Title says it all.

The two Nelson ships just never do real damage for their BR. Everything at their own BR guts the Nelsons turrets and their general armour, but the nelson struggles with Ise, Gneisenau, even downtiers like izmail and the other flat soviet ships. It guts battlecruisers (except gneisenau because it’s an outright pay-to-win at 7.7BR) but everything else it just doesn’t hurt them.

And then the Nelsons die to the same thing every time: three compartments go black and it dies to losing unsinkability. I almost never manage to cause the same effect in other ships, the Nelson can rarely even make one or two compartments turn black in other ships, it relies on extremely lucky ammo-detonations, not to mention it rarely causes flooding but always seems to suffer intense flooding itself.

Wtf am I doing wrong? I use my secondaries on their bridge to inflict crew losses, I aim for barbettes and below turrets with my main guns. Every time it’s clear I’m doing a third of the damage everyone else does in these ships.