Those numbers are waaay off, at least for Pascal cards. I don't know if you used the built in benchmark in the game (which is hardly representative of the actual performance), or a very simple wilderness run.
But I own a Asus GTX 1070Ti (which should sit between the 1070 and the 1080) updated with the latest nVidia driver, and with a mix of Original and Favor Quality (Med-High) my rig struggles to hold 60 FPS during gameplay at 1080p, with frequent drops to 30-40 even in mildly populated areas.
Meanwhile I can run any other contemporary game (The Division 2 or Ghost Recon Breakpoint for example) at much higher framerate with Ultra settings and minimum tweaks (80-90 FPS if I left them uncapped, permanent 60FPS without dips if I lock the framerate)
So here's the thing: you have to provide full system specs or comparisons basically become meaningless. This is why we detail the full specs of the test PCs. My test rigs had 32GB of RAM, running at DDR4-3600 speeds. I'm using a 2TB M.2 NVMe SSD. I've got Core i9-9900K (and the other CPUs, but those weren't tested with the GTX 1070 or 1080). I also am running a 'clean' OS. Do you have other apps or utilities open? Did you do a clean driver install? All of these things matter if you want to get consistent results that others could replicate.
Then you have to provide actual benchmark results at the same settings used for our tests. All you say is that your PC "struggles to hold 60 FPS during gameplay at 1080p, with frequent drops to 30-40..." According to my tests, the GTX 1070 averaged 74 fps, but with 99 percentile results of just 50 fps -- at 1080p high. If you have a slower PC on the CPU, RAM, or storage than what I used, that would be absolutely consistent with dips into the 30-40 fps range.
If you want to say the built-in benchmark results are meaningless, run the benchmark on your PC and provide a specific result. What does the benchmark give you for average and minimum fps? (You'll need to use a utility like OCAT to log results.) Then do a "wilderness run" and also log frametimes. Then send precise details on where you're testing and how you tested and someone else could corroborate the results.
From what I saw in testing, the benchmark may not fully represent all areas of the game, but it's repeatable and consistent. That's mostly why I used it. It's a baseline measurement -- there are areas that will run worse than the benchmark, others will run better, but it's a starting point. Also, the camera flyby of the city in the benchmark means lots of fast scene transitions, leading to generally lower minimum fps results.
But because people love to try and throw shade, let me provide some specific results. You have the earlier benchmark numbers for the GTX 1070, but here's a full set of data, using 1080p Favor Quality (high), using the built-in benchmark vs. me running around the wilderness (near the beginning of the game):
1070 @ 1080p High | Avg | Avg Min | 50th | 55th | 60th | 65th | 70th | 75th | 80th | 85th | 90th | 95th | 97th | 98th | 99th | 99.9th | Min |
Built-in Run 1 | 75.7 | 50.3 | 75.8 | 75.1 | 74.3 | 73.5 | 72.6 | 71.6 | 70.3 | 68.6 | 65.8 | 56.9 | 54.1 | 52 | 49.5 | 45.7 | 29.5 |
Built-in Run 2 | 75.2 | 50.3 | 75.3 | 74.5 | 73.7 | 72.9 | 72 | 71 | 69.8 | 67.9 | 65 | 56.3 | 53.7 | 51.8 | 49.6 | 46 | 27.1 |
Manual Run 1 | 67.3 | 59.5 | 67.2 | 66.7 | 66.2 | 65.8 | 65.3 | 64.9 | 64.4 | 63.8 | 63.1 | 62.1 | 61.4 | 60.8 | 59.9 | 55.7 | 33.1 |
Manual Run 2 | 66.5 | 58.6 | 66.5 | 66.2 | 65.8 | 65.4 | 65 | 64.5 | 64 | 63.4 | 62.7 | 61.5 | 60.7 | 59.9 | 58.7 | 54.1 | 42.1 |
So, the benchmark in this case is 13% faster than where I tested. That's a measurable difference, but it's not particularly meaningful. More importantly, look at the minimum FPS results. The benchmark is 14% slower than the manual test, mostly because of the fast scene transitions. Perhaps most importantly, the benchmark cuts the amount of effort to generate these articles down by 66%. I can start the test and go to another PC and start the test (in offline mode, naturally), and then go to a third PC and start the test. Which is how I was able to run a huge suite of test cards in a relatively short time.
Anyway, these performance analysis articles are provided largely as a service to readers. You now have precise measurements on how the game runs. I ran every benchmark at least twice, discarding the first result as it's usually a bit higher thanks to GPU boost clocks. I restarted the game between each settings change. If there was a major discrepancy between runs, or if numbers looked wrong, I'd verify the result with additional tests.
With a Core i9-9900K and a GTX 1070 FE, plus 32GB RAM and a fast 2TB SSD, running on a clean OS, I got average performance above 60 fps at 1080p high, and a bit of tweaking should get minimums above 60 as well. If you're getting substantially worse performance on similar specs, it's possibly software or drivers. More likely, it's software, drivers, and/or differences in hardware.