Walker would certainly be a vast improvement over what we have now. Hell, Jimmy Carter would be a vast improvement over what we have now, but that is because "what we have now" is setting the bar too damned low.
I think Walker could do a good job. He reminds me somewhat of Harry Truman. Of course, Truman got a lot of instant foreign policy credibility by dropping a couple of nukes and ending WWII.
I would take him over the rest of the field after Cruz.
I don’t remember Truman but really enjoyed visiting his home and Presidential memorial.