You're statement is true but I don't think that's what the Nikon FB post is saying. While you're suggesting two different photographers each with different equipment the statement from Nikon is comparing one photographer using different equipment... the implication being higher versus lower quality equipment in the hands of the same person Question then is if any given photographer would take better pictures with better equipment. I don't think that's necessarily true... depends whether the photographer or the equipment is the limiting factor (i.e. the weakest link). If the person has never used anything other than a camera phone they might not even be able to turn a DSLR on and attach the lens so they won't get a picture at all. In the hands of a pro, it might be fair to say that a he/she will almost always get a better picture with a better camera and lens (better meaning better suited to the type of picture being taken of course).
You reminded me about a comment which is often made in cycling: it's "90% rider and 10% bike". Putting me on a fancy Colnago will not make me win the TdF. However, in a pro race, that 10% counts, and it counts for a lot, because races are determined on seconds or less.
Yervant (or name your favourite pro photog) would be able to do produce some very good photos with a 600D and a kit lens, I am sure, but to compete in the market at the level which he does, he needs the very best equipment.
There is no substitute for skill, as others have pointed out, but at the highest levels of performance, equipment can make that small (even minute) difference that separates one photographer, or cyclist, or racing driver, etc. from another.
Put the other way around - putting me on an expensive Colnago is, right now, about as useful as putting lipstick on a pig.