Depends on who you ask pertaining to disadvantages.
Some might say--harder to steer with long waterline & little rocker - I say learn to use your boat properly.
By leaning a bit , thereby getting front and rear out of the water slightly AND using the rudder (SmartTrack)
I can turn my 18 foot long Epic Endurance quite well.
They do offer the advantage of speed. I think it's a case of different boats for different purposes. A "greenland" style kayak generally has a lot better rocker. That's why you don't see a whole lot of "plumb bow" kayaks in the surf.
Watched the video. Going out through the waves isn't the problem. Coming back in is. Kayaks with no rocker make it a lot easier to faceplant in the surf. I agree that something with no rocker will be faster. Kayaks with no rocker have a longer water line than those with rocker. That makes for increased speed.
If you're interested in this, read Nick Schade's book, "The Strip Built Kayak". It goes into some of the engineering and physics of kayak design and is pretty interesting.
That's a bit of an oversimplification. For those of us who's sea kayaking involves ocean paddling in rough conditions, Greenland style boats work awesome. I rarely paddle lakes or calm water, I paddle on the ocean, and in rough conditions, I bet I can hang easily with a boat like the epic in a boat like a Wilderness Systems Tempest.
And I land and launch through the surf on nearly every paddle. And I like to play in rock gardens and sea caves.
That "Porsche" might be fun on the autobahn or a racetrack, but I'll take a Range Rover any day. Far more versatile, will hang with the Porsche in most real world conditions, and can handle some rough stuff.