Yes, but it's sustaining those kilos. Gravity comes into effect.
Your argument displays logic, but it is in effect arguing the inaccurate. Otherwise you'd see André Greipel outclimbing José Rujano. Why are the light guys usually better climbers? Magic? The effect of increasing weight multiplies gravity's effect on you. Hence why a real life King Kong could never exist - a gorilla that size would collapse onto itself and be unable to stand.
The other thing is getting to that peak wattage. A heavier rider displays more inertia, which means that a lighter rider can accelerate more quickly than a heavier rider. Riding uphill, momentum (which is something a heavier rider has in their favour) is far less of a factor. Plus you have the increased drag factor in larger riders; something that is usually compensated for and more in a flat time trial or descent (again, gravity), but is harder to compromise in an ascent.
There isn't any hating on Tony Martin. He could well turn into a decent top 10 GT rider à la Leipheimer, Kirchen, Wiggins et al. He's fearsome over one week, because his ITT is so strong he can pull out a lead and stay with all but the best on the climbs. But three week GTs have longer climbs. And more of them.
Martin also suffers in the same way as most GT contenders in his vein (the likes of Evans, though Evans is a better climber and weaker TTer than Martin) in that the GT best suited to his skills is the Tour; the Vuelta and Giro both feature steeper climbs and a climb-TT balance more weighted in favour of the climber than the Tour - plus the types of climbs in the Tour are more regular and gradual which allows the TT-focused rider to hold on longer. Unfortunately, the Tour is also where absolutely everybody comes out to play.
The other problem of course, as already mentioned, is that short of holding the maillot jaune two days from the end of the race, NOTHING gets you out of sprint train duties at HTC (see Velits in the Vuelta), which means he'll be expending needless energy for the green jersey while the other GC candidates are chilling.