To start, it might be worth reviewing the recommended antenna traces for wireless ICs, since vendors often provide precomputed and validated reference designs in their data sheets. These are often what are made into breakout boards, and there’s a lot which can be learned by what these reference designs take into consideration.

I’ve not specifically done PCB designs with antennas, but I have done my own designs for high-speed differential signals, where the impedance of two traces have to be consistent along their length, whether side-by-side or on opposite sides of the PCB. As you observed, KiCAD can do a lot of this computation but good antenna design means even the pads that attach to the IC also need to be impedance-matched. And that requires both an understanding of where problems arise (eg when traces turn a corner), how to compute the effects (using KiCAD’s features), and whether the issue might not even make a big difference in overall performance.