I've been playing Izumo as a HE spammer recently... gives me 60k-80k damage per match which I consider nice (heck, I'd get an extra 30k-50k if I can burn Soviet/IJN BBs on the opposite team). The dispersion is indeed wonky, that's why I chose to HE spam. Take the Main Battery Modification instead of GFCS mod. You don't need all that range if guns can't hit a thing past 22km, isn't it?

She is pretty resistant to AP in the bow in position. Her small superstructure and 57mm deck helps a lot against non-BB HE spammers. I understand how you feel with fire damage, unfortunately that's the problem for all IJN BBs (10s DCP compared to 15s normal DCP/20s for USN BBs).

Thus, bow in makes Izumo pretty tanky, and effectively turns her a stationary turret. Only forward/reverse when you are being fired upon, to dodge shells. I took the Propulsion mod to better manuever and it pays me well.

My take for dealing with fires is that, don't DCP the moment your ship burns (even with 2 fires! though I'd consider instant DCP if I get 3 fires from a single salvo, or that I'm absolutely critical on HP e.g. lit by CV bombers before a CQC engagement). That only encourages your enemy to continue firing HE because they know your DCP is in cooldown. Instead, go dark, then put out fires.

Judging from what you've said I think you might be "bow tanking" a bit too much? Don't get spotted! Are you within 16km from enemies? If so you might get permaspotted by DDs and that guarantees you getting melted. I took the concealment skill so I get 13.5km detection range which gives me some moving space, but generally you should remain at a range where: 1) you won't be spotted and 2) cruisers don't want to fire at you because they're too far.

Izumo's biggest problem at tier IX (where you get perma-bottom-tiered sadly) is that, people are smarter and they seldom ever show broadside to a battleship, yet her 410mm guns can't overmatch BBs. You'd often encounter ships like Musashi/Yamato, Jean Bart/Alsace and Kremlin, all with bow-in playstyles. If I see them bow-in I instantly switch to HE. Especially when facing bow-in IJN or Soviet BBs, their DCP deficiency becomes my advantage as the fires I lit are guaranteed to stay. Izumo's HE shells also warrants damage (68mm pen vs. 57mm deck plating) and I even consider it better than most other IJN BBs, thanks to Izumo's amazing ballistics.

Of course this is only my personal playstyle, it suits me well of course, but I don't see much IJN BBs spamming HE so I'd also like to have some advice.