Perhaps it's DX12 related? Civ6, for example, works better on most nVidia cards with DX11, things slow down and become choppy with DX12. I've heard this is true for games other than Civ6 - but keep in mind it only seems to be nVidia cards effected. DX12 seems to be optimized for AMD cards for some reason.
dx12 discussion in Civ6 forum:
https://forums.civfanatics.com/threads/so-what-would-the-dx12-do-for-me.605453/
It isn't actually that DX12 is optimized for AMD cards, but that AMD cards are, at a hardware level, optimized for DX12 (and the similar, earlier, Vulkan and Mantle APIs, the latter of which Civ Beyond Earth supports). It's a bit complex to get into, even if you are from a technical background, but from a practical level, all AMD cards since the HD 7000 series (early 2012) are designed such that they'll benefit from DX12 changes, whereas all nVIDIA cards prior to the 1000 series (mid-2016) will see limited benefit, if any, from DX12 over DX11. The lack of benefit isn't something nVIDIA can change with driver updates due to the nature of the hardware, although if things are noticeably worse, they may be able to at least get it up to par with DX11.
(Note this is based on my understanding of DX12 and the hardware from prior to this fall; I haven't examined the Civ6 case in particular in detail)
This does mean that if you're buying a card today and, for whatever reason (maybe cards offered in a laptop) are comparing, say, a Radeon R9 290M to a GTX 965M or 970M, the AMD card will likely get a bit better longevity with DX12 games (this doesn't apply for the 1000-series nVIDIA cards). You might think that makes AMD smart, but they wound up introducing the capability to take advantage of DX12 several years before it became mainstream, so the actual benefit to them of being ahead of the times was likely negligible - it wasn't really until this summer than DX12 started to be prominent enough for more than a handful of people to care, and that coincided closely with when nVIDIA's cards that can take proper advantage of it debuted.
Although it wasn't all bad for AMD; their chips in the XBox One and PS4 also had these capabilities, and DX12-like programming has been possible in them since they came out. So it may have been an advantage in helping them land those deals. Perhaps not the deciding factor, but it likely did help, particularly as both consoles have many-core-but-slow-per-core CPUs of the sort that aren't amazing with DX11, but are at significantly less of a disadvantage with DX12/Mantle/Vulkan/etc.
As for the initial post, I suspect the game "optimization" increased the graphics settings, but to a level beyond what is actually ideal. I quit using the game "optimization" programs, for either GPU vendor's cards, very quickly after I first encountered them being bundled with drivers (un-checking them on install or uninstalling them after driver install), as they generally favor pretty graphics over smooth, fluid gameplay. And the settings in the screen shot do look daunting, even for a card as beefy as a GTX 970. If it, say, kicking Anisotropic from 4X to 16X, and Shadows from Medium to High, that could have a noticeable impact on frame rate, particularly at 4K resolution. If it kicked it from 1080p up to 4K, that would definitely have a noticeable impact. I'm curious if the problem being fixed really was purely a driver change, or if it got re-optimized to settings that are less extreme. While I'm sure the 970 can run Path of Exile at 4K, running it at 4K with very intensive options such as max anisotropic and post-processing is asking a fair amount for any card.
