And they are completely wrong. I've been using class 3 with perfect results for quite a while.
The problem though is that unless you have Guardian Reinforcements, you have ZERO protection from the caustic attacks, which is about 95% of the damage that Scouts do. That's why the AXI initiative tells you to use class 5 because they repair and decontaminate quicker.
If you're running the Guardian Reinforcements, you don't need that because not only do you have over 20% resistance to all caustic damage, it protects your modules as well because they can't get through your hull to begin with.
I usually can take 8 or 10 attacks from a scout before they even land a shot that contaminates my ship. After that, I lose about 1 hit point ever two or three minutes. That gives me plenty of time to just keep on fighting until I get a break.
By then, I'm probably at 95 or 96%, so I launch a decontaminator limpet and that repairs me right back up and I go right back in to fight some more.
Back when I used conventional hull reinforcements, I'd get infected instantly. Several times. My hull would drop at 1% every 10 seconds instead of 2 minutes. It also took a lot longer to decontaminate and repair, so I carried a class 6 storage rack full of limpets.
Going with the Guardian Hull Reinforcements was the single best thing I ever did to a ship. It really does make a night and day difference in how tough the ship is against Scouts.
I just compared my Chieftain running a lot of grade 5 engineered heavy duty deep plate hull reinforcements with using Guardian Hull Reinforcements instead. Now, my build took a lot of time in collecting materials to achieve, but the absolute and caustic hull hit points are both 4119.
With Guardian Hull Reinforcements instead my absolute hull hit points are 3199 and caustic 3928.
In battle I actually don't need to rush at burning off the caustic goo as the hull strength drops so slowly.
I don't seem to have a reason to switch to Guardian Hull Reinforcements now that I've gone to the granted greater effort of collecting materials to do regular heavy duty deep plate engineering.
Or am I missing something the numbers don't show?
A bit of searching shows there is a factor I'm missing.
Repair limpets. I don't use them on my Chieftain, but if you do, one limpet repairing a smaller amount of absolute hull effectively repairs a far greater amount of caustic hit points due to the effect of the resistances. This might explain why a class 3 repair / decontamination limpet controller is more effective for you that would normally be expected.
I find this interesting because if I were to do a Corvette build for AX combat I would be fitting repair and decontamination limpet capability, whether a multi-limpet controller or separate controllers.
I don't think I'll change the Chieftain build unless I suddenly get the skills to take on higher tier Interceptors, though.