It’s doubtful Britain was the “premier power”. Probably had the best navy, and the best anti-tank trap (the Channel), but the Wehrmacht and the Luftwaffe were both ahead of the British Army and the RAF by 1939. That’s why the British relied so heavily on the alliance with France: the French Army and the British Army were both necessary to match German land forces. It was also a factor in the appeasement debate: Chamberlain and the British government realised they needed time to catch up to Germany.
The other point, though, in that Hitler seemed to expect that the British would join him, because they were Germanic (mongrel Germanic, in his view, but Germanic), and therefore a natural ally for Germany. Britain was also opposed to Bolshevism. He hoped that Britain would join him in the fight against the Slavic Bolsheviks, as a junior partner in an Aryan alliance.
That may have been the explanation for the “Stop” order in June of 1940. Hitler stopped his troops from attacking the retreating British forces, which helped the evacuation at Dunkirk. In theory is that he wanted Britain to see that he didn’t want to defeat them entirely, but co-opt them.