This depends on the model, e.g., the non-entry level Forerunner series watches have had training load-related metrics for a while now. That said, Garmin is mainly a cardio watch, and by extension the Apple training load metrics seems to be giving a more presentable UX to the "default"[1] approach to cardio training load.

[1] https://evokeendurance.com/a-new-and-better-look-at-training...