Based off current PS5 sales, it's still humming along fine. Gaming division sales are sky high and profits are good too. Profit margins are squeezed past bunch of years due to Sony's dev costs and GAAS push.
So for now I dont see any porting effect killing sales.
BUT as some people have said (like yourself), when it comes to PS6 time and Sony releases a good system at a decent price etc.... and PS6 sales tank. And you got a lot of core gamers on forums saying (anecdotal in the grand scheme of things, but forum users are going to lean early adopters) that's the right time to jump ship and transition to PC or Switch 2 or AMD Xbox whatever gadget then yes, I'll agree the porting has negatively affected PS if thats the only logical factor left.
Or if somehow PS5 sales tank next few years before launch as people go to PC or Xbox as more ports come and there's no other logical reason, then I'll agree too.
I think the problem with PS5 sales being only status quo with PS4 is more about hiked up prices and their shift to GAAS. So some gamers have jumped to another platform. Or just milking PS4 to the last drop as a system that's good enough. If PS5 was $200 cheaper you'd get way more sales. Same with Xbox. As crazy as this is, prices have gone UP. At this time 4 years in, PS4 was down to $300. When you get to low prices like this is when some people buy two systems. One for the living room one for the bedroom. At $500 US, I dont think too many people are doubling up PS5 systems. So for PS5 sales to be pretty similar to PS4 is solid.
PS5 Pro is $700. Let's say PS6 is $700-800 for sake of argument and sales trend worse than PS5. It can be argued pricing is getting out of whack killing sales. Not ports.
Who knows. We'll have to see in a couple years what the sales are like compared to all the variables that can affect it.