Nope. You seem to be ignoring it yourself. Those reasons are what would make it more likely for Sony to launch remasters/ports of the higher selling games on PS5 instead of giving free BC and hoping to sell GOTY editions. It isn't even nearly the same effect in sales. If it was, Sony wouldn't be doing all the remasters and doing this route. They can do it because they are in a position of power and market leadership. If they needed to gain market favor them they could go the less profitable route with free BC.
SO I'll repeat myself. Sony doesn't have any incentive to get free-BC on PS5 (even more considering they saying that there is low use, coming from a company that put full BC in PS2 and PS3) when they profit much more from re-releases. So even if PS5 could get BC very easily they will rather make a very easily port, with less downgraded assets (already made for original game). The infamous patent for the easier upscalling is more likely to be used to make remasters cheapers to make than they just giving it away.
There is not a chance on earth that the PS5 doesnt have native BC with the PS4. Not a a chance at all.
It will be platform suicide by sony. Especially considering how big digital distribution has become now. How does sony explain t the 100M people that would have owned the PS4 that their PS4 games cant work on the PS5 all the while the next XB is running XB1 games.
Make no mistake. PS5 will support full native BC the very same way the PS2 supported "improved" BC with the PS1. We will see far fewer remasters next gen and mre "remakes". The "remaster" will be a natural by product of just having a much more powerful X86 hardware (which the PS4 also is so by default that already means native support). If we are lucky we may et some patches for a few older titles adding in 4k textures and stuff. Highly unlikely though.