At the height of the British Empire, the Royal Navy was overwhelmingly more powerful than any other navy in the world. The US Navy today is overwhelmingly more powerful than any other navy in the world, too, but not to the same extent.
The Royal Navy was so powerful that after Britain decided to outlaw slavery, the RN policed the entire world's oceans to make sure the slave trade was really abolished. Their global reach was so pervasive that they passed a law and then just FORCED the entire world to follow it -- think of that!
As well, I'm not sure what you mean by saying that Britain didn't have command of both the Atlantic and Pacific. It certainly did! British territory across the Pacific, some of which it still owns, included Australia, Pitcairn, New Zealand, Singapore, Hong Kong, Fiji, Vanuatu, Kiribati, the New Hebrides and the Solomon Islands.
In the Atlantic, the British owned (and still own) Bermuda, the Virgin Islands, Gibraltar, Canada, Nova Scotia, the Bahamas, Jamaica, British Guyana, so much of Africa I don't even know where to start, and of course the British Isles themselves.
In the Indian Ocean, Britain owned (and also somewhat still owns) India, Pakistan, Zanzibar, the Chagos Islands, Ceylon, the Arabian Peninsula, and South Africa.
In the Southern Ocean, the British owned parts of Antarctica, the Falkland Islands, Australia (again), and New Zealand.
In the Arctic Ocean, Britain owned Canada, Orkney, and Shetland.
So I'm not sure what you mean when you say Britain's reach didn't extend to two oceans.