Absolutely true. There are very few people in all of the region that follow where the Whitecaps are in the standings, etc.
As a relative newcomer to the area here's a few thoughts on the Whitecaps/Griffins dynamic:
1.) There's two Grand Rapids. One that prefers the suburbs and is more or less terrified of going downtown (omg the parking! omg the homeless people! omg! omg!) and then there's the other set that has no problem going downtown and figuring it out. The Whitecaps make the suburanists happy. The Griffins make the downtown set happy. So in that light, the current arrangement makes sense.
2.) Apparently the suburbanists are not as big as some of us think they are as the Griffins attendance continues to be strong-- 5th place in the league this year. Of course it's not an apples to apples comparison. Would the Caps attendance be better if the quality of play was higher? Probably, sure. But clearly people are willing to come downtown to see a minor league sports team, let alone consistently selling it out for big-name comedians/musicians/etc.
3.) As many have stated, the town is too big for Single A-- but indeed the stadium is lacking in location not in capacity (it's capacity is higher than most Eastern League AA teams). As a downtown-supporter I'd love to see a stadium built maybe where Charlie's Crab is or any other surface-lot desert in downtown GR so that the region's residents could make an evening of going to the ballpark in the summer like so many other cities have done successfully. Instead it's in an out of the way location (much like the mistake that Syracuse made when re-building their's out of the way all for the sake of parking), and that will always hold the franchise back. The first trick is to find property & funding for the stadium (a tall task), the second trick is to not scare the existing core suburbanists from coming and finding a way to placate them (parking packages, etc.). The restaurants and nightlife will take care of itself and fill in.
4.) There's less and less of a difference between AA and AAA these days. Most franchises use them nearly interchangeably for their prospects and getting the Tigers AA team would be a much bigger draw for local Tiger fans than low-A. In my view it would be the near-equivalent of landing the AAA team. Targeting Erie makes plenty of sense, but the devil is in the details and I know nothing of the details of their affiliation with the Tigers.