Snake has a weight of 113 which is the 3rd heaviest in the game. By comparison, Bowser is at 120, DK at 116, DDD at 112, Charizard at 110, Ganondorf at 109, and Samus at 108. I don' think this is totally unreasonable; Snake is just about as big as Ganondorf and has just as much heavy equipment. Saying it's a little more so he has 4 more weight (which is really not much) is reasonable. As per DDD and Charizard, remember both are built to fly so they're going to be a bit lighter than their size would indicate.
If you're curious, the low ends of weight is Jigglypuff at 68 with Squirtle and Mr. Game & Watch in second place with 75.