While neither the person who's purchased access for one specific digital product nor the person who subscribes to a paid payment plan for that same access actually own the product in question, you've neglected to mention something crucial regarding the lowest tier PlayStation Plus subscription plan. When that subscription plan has ended, any items they've redeemed "for free" (let it be known that they are, in fact, not free) become totally inaccessible. Meanwhile, for anyone who purchases direct access to an item, they don't have to worry about that. How long that access lasts, though, is another matter.
Also, saying that everyone who's directly purchased a digital product like the ones you've mentioned that have also been available as monthly PlayStation Plus games but do not subscribe to that plan has been manipulated seems disingenuous. I'm sure that, whether a digital store item was priced at $20 or $20 at a sales discount or however it's being marketed, plenty of people will just be happy to add the game to their collection for that price.