For tracking fitness improvements for cycling, you already have a great tool in the Compare tab like shown below:
The problem is that there is something equivalent missing for running and I know that pace or power/HR metric is already on your to-do list, but I understand this is quite a complex one to implement.
A possible quick alternative in my opinion would be to add the possibility to select LTHR and Threshold pace on the Y-axis in the Compare tab. In this manner, we could do FTP run workouts like the table below and plot out the LTHR and Threshold detected from the workout, which we manually have to adjust after the workout anyway to have properly defined training zones.
PS: Garmin watches have this guided “FTP test workouts” build-in which are quite handy if you perform them regularly to track progress.
Thanks for considering!