Indeed it would require a HUGE amount of power to reach such speeds underwater. No matter how big a gas "bubble" you might blow in front of the missile, something has to have some incredible horsepower to displace that much water at those speeds. The bubble only makes the skin slippery but something has to shove aside all that dense water, whether it's bubble or metal skin. Anyone who believes that a few gas bubbles can magically let something zip through dense water with little effort, well, then the laws of physics apparently don't apply to this device.
This device doesn't blow a bubble in front of itself. The design of the nose creates the bubble which the rest of the device passes through.
Yes, it does take a lot of power but the Russians have had such a missile for quite some time. The English name for theirs is the 'Squal'.
Russia is a leader in supercavitation technology and in 1977 fielded the Shkval (Squal) rocket torpedo, which can achieve speeds up to 200kts, or 100 meters per second (230 mph) through water. An advanced version of the Shkval is reportedly capable of 300kts speed.[70] This version reportedly was being tested on the Russian Oscar-class SSGN Kusk that sank in August 2000. The U.S., France and Germany also have supercavitating weapons research programs.Here's the link: Advanced weapons report
There was an article about these torpedoes in Scientific American quite a few years ago. They are not violating the laws of physics. They are not pushing aside anywhere near as much water as a submarine, though of course they move faster. The "bubble" is mainly formed through cavitation that begins at the narrow nose of the torpedo, although some designs also involve recirculation of rocket exhaust.
This torpedo technology has been around so long that I heard some time ago that the Russians were marketing their 1st generation designs to other countries.