You're kind of pre-supposing that the next gen games HAVE to be $70 aren't you? There's been cross gen games before where one version wasn't made any more or less expensive. Ever played the abomination that is Ghost Recon Advanced Warfighter on PS2?
Anyways this is a conversation gone over like a thousand times on these boards and elsewhere. All that said if you're going to make the argument that the rising cost of game development requires $70 games -- which I don't automatically accept as true -- there's literally no reason why the PS4 version shouldn't also be $70.
Regarding development costs...destruction all Stars was initially announced as a $70 game, then dropped to a $20 game before it had even left PS plus. Did development costs suddenly plummet 80%, I could go on all day about this, but it is what it is. The switch has already been flipped.
Destruction All-Stars is a case of a product showing it can't move at the price point listed and therefore has to be marked down quickly to minimize losses on the product.
I'll say this, I'm content paying $90 CAD if the product like most SIE exclusives such as Horizon:Zero Dawn, God of War, Ghost of Tsushima, Uncharted 4, Spider-Man, Last of Us part 2, etc live up to the high-standards SIE showed for their internal AAA titles and so far the 3 big PS5 SIE exclusives have been very well received (Returnal, Ratchet, and Demon Souls). I'm not lining up to pay it though for the next Fifa or Madden or a game I'm taking a chance on (I'll wait the 9 months for it to be marked down). The issue they've run into is legacy issues in that they avoided jumping prices mid-gen, and decided to do it at the start of the next gen. At the end of the day vote with your wallet. I will say though, Sony's games tend to avoid massive MTX, which is partially due to being primarily single player focuses cinematic games, but you are getting a complete product. I'll take that over a PS5 AC: Valhalla at an 80 dollar launch price but have a ton of the armour locked behind pre-order bonuses and microtransactions.