Why?
People in all walks of life put themselves through career changes in their 20's, 30's, 40's.
Playing baseball for a living when you're young doesn’t entitle you to a lifetime of retirement.
Current hitters aren't "so much better."
And Palmer would have the same training and data used to increase velocity today that others do. He was tremendous because he could pitch. He'd have the same ability today.
He just wouldn't get to pitch as much. Modern baseball theory is hopelessly lost in many respects. "Pitchers cant be allowed to pitch" is one example.
The 3rd base coach plays zero role in the decision to try to tag and advance from 2nd.
In fact the 3rd base coach plays zero role in most baserunning decisions.