Fabrication improvements mostly mean that processor will run cooler, so can run at higher frequency without burning. It does not improve the IPC of that processor.

It's not always being cooler per se that makes the difference; other problems such as electron tunnelling (we're getting well beyond my paygrade, there's a lot more) can be limited with a better hardware design (say tapeout) as well. But yes, you get better performance from being able to function at a higher frequency on a large die (with more heat, but that wasn't necessarily the limiting factor previously) or on a smaller die where the parts are now closer together and so take less time and energy (heat) to communicate. A better tapeout geography can mean fewer lost cycles waiting for this or that info to get where it's going and so actually increase useful IPC at least a bit.