Hang on. Even if you can't make up your mind which "expert predictions" to like....you're assuming the UK will remain the same, when there's a good chance that it won't. Scotland and Northern Ireland might vote to leave the UK, in hopes of remaining in the EU. (There could even be a "United Ireland" in the next decade, who knows.) Then you'd no longer be the 5th largest economy in the world.
And you'd support their moves toward independence -- for the same reasons you've given for Brexit -- even though it would mean breaking up the UK into smaller pieces, right?