I don't really think much/any of this will be a counter point as such, probably just 2 different roads to the same destination.
I think so too. Really, I use step ups because they're technically simple, easily expose ankle/hip/knee issues, get a training effect quickly, and have minimal deceleration issues like lunges (even static lunges) do. If I was running a gym and KPj showed up and squatted 60-year old clients, I'd have no issue with it. He's got sound reasoning and a plan. My plan just starts with single leg because everybody steps.
And yeah, even the 60-year old clients push the Prowler. They may walk an empty Econo Prowler for short distances, high handles only, but they use it. That exposes a lot of bent wrist pushing, flexion when confronting a load, ankle/hip/knee mobility/stability problems, etc. and get a training effect at the same time. Easy to scale, too - more yardage, more weight, etc.
And might I add in a recommendation for barbell pushups? You can scale them to anyone, they don't have the wall in the way like wall pushups, they teach pulling the bar in/scapular retraction well, and no one has an idea locked in their head about how to do one. Plus they are very easy to progress, one power rack peg at a time.