You’ve increased the load on the CPU, which while this should not generally show up as inferior fps, it can make the system more unpredictable with performance. You could try upping the resolution, maybe super-sampling and seeing if that creates a better balance.
A hell of a lot of folks on these forums have a 13900K and 4090 GPU, me included, so if you are actually worried about performance and not embarrassed to show you system specifications against your reported fps, then tell us what settings you are using and a screenshot showing the inbuilt MSFS fps and we’ll do a comparison for you.