I don't know how or when this whole non-sense about a sequel needing to be a completely different game came from but "fanboys are gonna fanboy" so...
unless, of course, a more of the same sequel is coming to their favorite box.
If Spiderman on PS4 was the first game and Miles Morales was just a stop-over spin-off to tide us over for the "real" sequel, then I don't think it's unreasonable to expect a major visual leap, especially when the sequel is on a console much more powerful than the PS4.
Knowing the visual jump between TLOU1 and TLOU2, it would be hard to get excited if TLOU3 on PS5 ended up being
only a slight improvement over TLOU2. Same thing here.
If Spiderman Miles Morales had been PS5-only
and a gigantic leap over PS4 Spiderman and then Spiderman 2 was building off Miles Morales then no problem, but that's not what we have here.
I'd actually argue the polar opposite to what you're saying, i.e. when did we suddenly stop expecting major leaps between consoles? People said the PS4 was terribly underpowered from the get-go and yet we still had visual bangers a few years in (relative to PS3). Hell, look at stuff like Ryse Son of Rome, what an absolute visual powerhouse and it was available
at launch.
PS5 launched as a system with respectable performance (not top of the line PC-beating specs but consoles never are) and yet now it's somehow criminal to expect meaningful visual leaps?
I think what's happened is that, because of the relative of ease of putting games on both current and last gen (because they're both x86-based and both AMD, as opposed to PS4 x86 versus the Cell processor in the PS3), the executive teams (ie people controlling money and budgets) at these publishers/platforms have decided "
fuck it, who cares about technical innovation, let's keep cross-gen going for as long as possible so we can milk the last gen installed base".