If casual players care about 4k then the PS4 and X1 wouldn't have constantly outsold the Pro and X1X after release, those people have been playing at lower resolution all this time regardless.
I'm in the UK the difference is actually £110 here if you can find a PS5 DE, that's a lot of money to some people in a country that looks like it is looking at big inflation in the short term. Also this Xmas what will actually be on the shelves? People going to buy a new console this festive season may be faced with just one choice due to shortages and that will be the more available Series S. Also not only is the PS5 DE £110 more expensive and not readily available but you are totally tied to that very expensive Sony store, with Series consoles third party keys are available at sometimes big discounts even undercutting disc copies, you can also get keys worldwide and activate them on your UK account making some serious savings, the cost difference between the two just grows from that £110. The only person I know with a PS5 DE told me he wished he had waited for the disc version as the store prices were just too much.
As for playing on last gen machines, if you read my post I said when the big hitters stop being available for last gen machines, will GTA VI be on PS4 or X1, I think not so that's the point people will move on.
As for developers, we've covered this numerous times, Series S just fits into the GDK now and looking at the lowest PC specs for releases this year it will be a very long time before Series S is down there at 1080p, so that's a non issue.