See, I question if that 70/30 is just due to fanbases being spread (over several entries) rather than a new audience being attracted on a different platform. Its tough to differentiate and so I think the easiest indicator of a breakthrough would be by looking at PS4 numbers.
Do you know the split of console/PC for W3?
I don't see why anyone would base market health on the performance of one title, let alone an outlier.
I don't think Dark Souls 3 found a new audience. I think Dark Souls 1 did, and we still see that reflected today in From Software releasing games for XB1 and finding success there (and the series in general finding a lot more success than almost every Japanese PS4 games to boot).
Bloodborne pretty clearly did as well, as I'll get to in a minute.
Let's look at the debut sales trend in the US:
Demon's Souls (PS3) - 156K
Dark Souls 1 (PS3) - 190K
Dark Souls 1 (360) - 160K
Dark Souls 2 (PS3) - 178.5K
Dark Souls 2 (360) - 171.5K
Bloodborne (PS4) - 389,000
Dark Souls 3 (PS4) - 353,000
Dark Souls 3 (XBO) - 151,000
(Note that the last two games here will have a significant 20%+ digital component to boot, but we can ignore that and largely come to the same conclusions below.)
You will notice that Xbox sales are very stable, and that the PlayStation sales are largely similar to Demon's Souls until Bloodborne came out, at which point it grew a lot, and the audience was still there for Dark Souls 3.
This is even before we get to the series having multimillion unit success on PC, which is another sign of it reaching a major audience that very few Japanese games do.
For a lot of Japanese games, they don't really see a point in releasing on Xbox anymore because the PC gets them an expanded audience and they don't feel there's much likelihood that their games has notable appeal among people who use neither PS4 nor PC. And, you know, most of them are niche titles so I don't think it really matters.
Where I think it hurts for FFXV to not find success there is that this game clearly exists in a different galaxy than most Japanese games in terms of sales expectations, and thus only having any appeal to the PlayStation audience suggests they're missing out on audiences like Xbox and PC that would help them get there.
You can certainly have success while getting 90%+ of your sales on PlayStation, but there becomes the question of why that's happening when it's not true for other products, and how much the factors that are limiting your appeal elsewhere are also limiting your appeal on PS4.
Tabata notes that, while it's an aspiration and not a sales goal, the team's pie in the sky target is 10 million units. We're instead having discussions of how it will stack up to FF13, a game that did 6.2 million upfront and eventually climbed to 7.5-8 million copies, and seeing that it's most likely going to get to less than half of what that game did in Japan.
I could be off base here, but so far I don't feel there's huge positive signs for the title to be a breakout hit beyond what it's done overseas with the past game, suggesting it will continue the series' decline overall, and I don't think that's a positive sign given how much support Square Enix has given the game. It's not even assured there will be another mainline title this generation, and who knows what the market conditions will be like then.