That means that the dozens of board games released each year are going to split a much smaller chunk of the admittedly larger pie.
You're just guessing wildly here.
One particular data point shows the opposite - a boardgames Kickstarter will typically get much more than an RPG Kickstarter. In fact, the top boardgame Kickstarter is 8 times more successful than the top RPG one (and three weeks ago, before 7th Sea, it was 16 times bigger). That's not smaller chunks of pie. That's bigger chunks of pie. 8 times bigger.