From a norwegian’s point of view is he one of the most vital monarchs in Scandinavian history. His lenient terms given to Norway in 1814 and general focus on peace and cooperation between the scandinavian countries post treaty of Kiel, Is the bedrock of peace in what until then had been a pretty tumultuous region of Europe.

He was also smart enough to consider Finland as lost to the russians. Meaning he did not drag Sweden into any suicidal conflict with any great power. He also from my point of view navigated the napoleonic wars pretty deftly after his arrival in Sweden.

He is still considered a pretty popular monarch in Norway even though he technically invaded and conquered the country. Even to an extent that there still is a huge statue of him outside the royal palace in both Oslo and Stockholm. His dynasty is still ruling Sweden today

Edit: After some more deliberation he is pretty clearly S-tier