Is strength a good progress indicator?

Strength is indeed a good indicator of progress. According to Sal Di Stefano, if you are getting stronger—whether it's doing more reps, lifting more weight, or feeling more stable during exercises—it typically means that most aspects of your training are correct. It's an objective measure, unlike subjective assessments such as changes in appearance, which can be deceptive 1.

Justin Andrews also mentions that strength is probably the best metric for overall health and progress, reinforcing the point that its objectivity offers clear proof of whether your fitness alignment is effective 1.