You're the one who said Sony is clueless with their MP/GaaS games, not me. I shown that they are very successful so far (I didn't count Destiny 2 because it was acquired).
You also mentioned that Helldivers 2 will compete against them, not me. I shown they are very different games targeting different player types. So they don't really compete against each other. As of now Sony doesn't have any MP Third Person Shooter, specially one focused on coop.
This is a sequel of a pretty successful small game, but now is making its jump to a more AAA Gears like concept.
Big pubilshers like Sony make market research and know the size and potential sales of each niche, so they spend a proportional marketing on each game. If they know that a smaller project to cover a smaller niche will only sell a few millions doesn't make any sense to spend on it the same marketing budget than in God of War or Fortnite. It would be to waste money.
As far as I know they never announced the complete sales of any Ratchet game. I also don't remember to see any Ratchet appearing consistently high in sales rankings, which often means less than 4-5M copies sold.
I think Rift Apart and the PS4 game didn't and won't sell 7-8M. I'd bet it's more realistic to expect them to sell a bit more than the half of that in case of them ending being the best selling games in the series.