Framerate tuning

I have an old macbook that’s running the game on low settings at 1024x768 and it’s a consistent and smooth experience. This computer is from 2015 and is using an Intel Iris Pro graphics (integrated).

The other machine is running a Ryzen 1700 and GTX 1070 at 2560x1440 but when there’s s lot of things going on the framerate drops to less than 30 fps while at the same time I can see the same game on the macbook running the lowest settings at a consistent framerate.

Why is the slower machine (the macbook at low settings) doing so much better? I’m trying to strike a balance between performance and quality but I don’t understand what settings have the biggest impact. This problem is mostly related to the unit count. The more stuff on screen, the worse the fps which isn’t all that strange but when considering the disparity between these two systems it’s not reasonable that the framerate is that much lower on a much much beefier system even if it’s running at a higher resolution?