Maybe but making a game isn't like baking a cake. It doesn't necessarily scale in the same way that something like that does. But it does make some sense. But the thing is, there are ways of offsetting certain...uh...scaleables. Nowadays we have middlewares to streamline certain things like animations. But your theory does make a lot of sense. Bigger will always take more time than smaller when it comes to development.
But it's not necessarily the big things that are going to mess up your dev timeline. Implementing something small might sound easy, but might wind up actually taking up huge chunks of your time. Focusing on minutae is important when crafting an atmospheric environment, but it takes a long time. Putting realistic mold on the bread in RE 7 is a very small detail, but takes time. And the more photo-realistic it is, the more time it's going to take to render.
That said, I wouldn't assume to know anything about the development of this game and what tools are being used to create it beyond the Dagon engine which I think might have had something to do with the development cycle. I honestly have no idea what goes into building a new engine, but I've seen estimates range from between 1 and 3 years.
But you know, Dagon's been built! The hard part is done. All you have to do is take your assets and plunk them in. Easy peasy! People have a lot of misconceptions about how long it should take to make a game because DUDE, THERE'S A NEW CALL OF DUTY GAME EVERY YEAR. The ONLY way that's even remotely possible is because those games are actually split up between two different studios who alternate every other year. And rest assured that when those studios are working on those games, they have hundreds of people working for them. Senscape, from what I can tell, really doesn't have anywhere near the number of employees working for them.
Lots of notable games have taken a long time to develop and release. Half Life 2 took 5 years and 40 million dollars to get released. 9 years for Team Fortress 2. LA Noire was 7 years in development. In fact, if you're interested in it, there were more than a few articles about what shitty conditions that game was produced under. Like this one for example: http://ca.ign.com/articles/2011/06/24/why-did-la-noire-take-seven-years-to-make
I mean, I don't necessarily want to make excuses for anyone, but even under the most optimal conditions, game development can still take a very long time. I wouldn't want to assume I know anything about the inner workings of Senscape, but long development cycles are nothing new in the industry and I sincerely doubt that will change into the future. Personally I hope it's not a Duke Nukem Forever situation where Senscape keeps trying to cram pointless new features into the game that don't belong there.