I took my time and still was on the lower end of 9 hours at the end of the campaign. I PURPOSELY spent time in Mercenaries and started a second playthrough just to rack up some hours, but it didn't feel like "here's everything you missed!", so the vast majority of people are probably going to clock around 9 hours and then not pick the game up again (perhaps until there's DLC).
I get that that's like half of RE4, but what about RE5, 6 and 7 or RE2Make? I remember RE4 being an outlier in being longer than the other games in the series I played. It would be helpful to get an idea of how it compares to the whole series and not just a single game.
While it's true most RE games clock in on the shorter side, we DO need to hold devs to higher standards, or in this case, at least RE4. Apparently, a lot of the game was influenced by RE4 except one of the most exceptional parts: content. However, RE5 and RE6 were both quite a bit longer, as I think RE5 was about 14 hours, and RE6 was about 17 hours. You can look all this stuff up, though, lol
Having said that, RE8 summarily comes in on the short side, even though there are shorter RE experiences. But this is 2021, we should expect our devs to be able to craft more detailed experiences considering the massively improved tech that is available. When a car went 0-60 in 6 seconds 30 years ago, that was "fast". Now, that's "slow". The times change, and one has to consider that many other games costing the same amount provide far longer experiences or offer much more content. The "not every game has to be long" rhetoric is mostly coming from Sony fanboys who are trying to justify Sony's push for $70 games.