First off i'll say trust me when I say I know how she plays: As of writing this I've played 270 battles in her.
So now we know that we're getting Semi-AP with the upcoming Italian Cruiser line it should be a open and shut case that the Roma be changed to match this new shell type specifically as the original reason going around the forums when she was being added as for why she wont get her SAP is because they have no plans to ever add it. Yet here we are with it being added.
The reason it's a needed change is a two-fold answer:
1: Every ship armed with the Cannone da 381/50 Ansaldo M1934 guns (Roma, Littorio, and Vittorio Veneto) never fired nor carried a single round of High-Explosive rounds for their 15' guns. HE shells were designed and tested for them, but their fuses were deemed too sensitive and so the HE shells never saw production past testing. The fact that Roma was given HE to begin with did cause a bit of a slight controversy but it was quelled only because of the reason that SAP just wasn't going to be added. Yet now it is. So there's no reason a change to reflect this shouldn't be considered.
2: Currently Roma is severely lacking across the board when compared to her competitors at her tier (and even some a tier lower if we're honest).
She doesn't fit any role that feels like her own or actually works in the meta; The idea I can tell what WG intended with her was a close range stealthy (by BB standards) brawler, Problem is. that doesn't work given her stats. Her armor is too weak and citadel too exposed to get in close, which makes you feel you need to hang back, but your guns are too inaccurate to land any hits at anything past 12km, let alone 6-10 (where she'll still struggle to barely land 4 if you're lucky.) So it paradoxically makes you feel forced to get closer to do any damage but you know you cant get closer because of your armor layout and that everything will focus you down.
And so as it stands she doesn't have anything that makes her unique or anything that's her own, there's a ship that performs better than her in every category out there, and she's not a jack of all trades either, she's sadly just infuriatingly below average across the board. She's desperately in need of something to make her feel unique and perform at a similar level to her peers.
Honestly most of the issues I have always experienced when playing her that have kept me from loving her in game as much as I do historically, has to do with her guns. Which is rather ironic since historically they were one of her biggest strengths. And the fix to give her SAP not only makes sense historically, but practically, since no one uses her HE, and it would perform much better and allow her to have something to adequately fight back at her tier and be on a level playing field with her equal tier opponents rather than feeling like a tier 7.5 like she does now.