When you put it in that perspective, it becomes obvious. The British land forces would have been much weaker than the Werhmacht, since they left their equipment at Dunkirk. OTOH the RAF was a lot stronger in 1940 than the Luftwaffe was in 1944, and in 1940 the Royal Navy was also more powerful than the 1944 Kriegsmarine (tho the issue would have been decided primarily by the contest between the Luftwaffe and the RAF). It was far too close to being a fair fight to have been an attractive option for the German military.
The Germany Navy wasn’t strong enough to take Britain, building up the Kriegsmarine was not high on Hitler’s list. He thought the U-Boats were all he needed.
Germany had NO prospects of successfully invading the British Isles. They had no experience in amphibious operations, no equipment to successfully conduct an invasion, and no way to combat either the Royal Navy or the Royal Air Force.
If you read this link you’ll be shocked at how ridiculous German planning was:
http://www.johndclare.net/wwii6_sealion.htm