OP doesn't specify how long he was playing for, nor the resolution. Anandtech doesn't specify that they tested gaming under Boot Camp and with a starting price of $2400 reaching for the screwdrivers is likely not the first recourse of action.
There was a post not so long ago; one of the members was convinced that poor application of thermal was the root cause of his high temps and he did a tremendous job of documenting everything pictorially including Apples less than perfect application of the past, yep it looked a mess, all over the place. Careful cleaning and precise application of a high quality paste net result? nada, nothing realistically no real tangible benefit. His machine did run a little cooler and once again being an older system cleaning the cooling system may well have brought the bulk of the benefit. I in his own words or thereabouts it simply wasn't worth it
Safe to say Apple have moved on with quality control, and it`s often prudent to check how much gas is in the tank before you start ripping the motor out

i dont discout your theory however it wouldn't be first on my list and likely one of the last. For all we know the OP could have been playing the game on his bed, effectively blocking air circulation, of course if he`s is happy to "have at it" with the Pentalobe screwdriver then we will all happily wait on the pictures