Further to your point, many versions of a 'Grand Unification Theory' doesn't even include gravity because they couldn't make it fit. Kind of making it a failure on the 'grand unification' bit. There are some versions of GUT that include gravity as a constant but all versions include many variables that need to be tweaked for different 'situations' to make it work. In fact, one might even surmise that if we can actually figure out gravity, we might be very close to proving which school of physics has been correct all along.

Of course, I'm so under-qualified to comment on such things that I probably shouldn't even be trying to post such information. But, it's fun to ponder sometimes, even if we will never be the ones to figure it all out. In short, all I really wanted to do was comment on how gravity is actually the thorn in the side of physicists everywhere.

With great power comes Awesome irresponsibility.