When it comes to quantifying overall training "load" it really doesn't get any better than:
1) monitoring time spent going hard in significant/meaningful chunks (i.e - if it feels hard, then it is hard. so, yeah, log it as such...)
2) monitoring KJ's of external work (yeah, strava gets it good enough for solo rides)
What about the gizmo power metrics people seem to be agog about??? Well, caveat emptor...they are redundant at best and misleading at worst.
The benefit of training while a power meter is attached to your bike is kinda questionable in the strava + stopwatch + bathroom scale era, eh? Sure, I still train while a power meter is attached to my bike, but, then again, I trained while a HR monitor was attached to my body for years as well...I'm probably just a slow learner!