The US Military readiness ebbs and flows, like any other organization. Based on the leadership culture, it flows from the generals and admirals to the privates and seamen.
I was in Jimmy Carter's army. The leadership climate sucked. Carter wasn't concerned with military strength, and the leadership climate from the top amplified that fact. Small unit leaders did what they could, but when you don't have fuel to run tanks, or enough ammunition to conduct training, it's hard to keep any unit trained. Lack of purpose erodes readiness just as surely as a raging stream erodes it's banks.
The Heritage Foundation gives an annual assessment of military strength. This year's assessment isn't pretty. It seems that readiness under Biden is starting to look like readiness under Carter. It sucks.
The article is behind a paywall, but you can download the full report from the Heritage Foundation.