A single cutscene tells you nothing, you could run it perfectly and suffer slowdowns in another part of the game. I actually think it's rocket science because not only textures and graphics are calculated in the game, and not only graphics affetcs performance. Especially in an open world game. You can heavily mod Skyrim (for example), load the game, turn around few times and everything perfect. You move along the map and soon issues are coming and game is stuttering bad. In a FPS game it could be different. I think that in this case there are too much things to be implemented in the benchmark to make it worth the time spent. But if your knowledge is far superior than you're welcome to share and proof it
Maybe I was wrong saying it has never been done. But I still believe that's useless. You start your game and see how it performs, if the game comes at release with its own benchmark, even better. If you have to upgrqade your pc you can do it AFTER the game is released. And by the way drivers will deliver better performances in a few weeks. This hurry to know and upgrade is really unnecessary IMO but of course this is my point of view
