In my mind, people who give up mid-match are worse than the AFKers. When you notice that someone is AFK at the beginning of a match, you already know that it's an uphill battle from the start. Fair enough, it's a loss, let's do our best anyway and move on. When someone just leaves mid-match because the first two minutes of a match didn't go well, it makes it incredibly frustrating for the remaining players on that team since any chance you might've had to start a comeback is now gone.
I did have a match in Rainmaker yesterday though in which someone would just hang out hidden in our ink close to our base, despite the opponents not making any pushes whatsoever. Might've been a kid, but that wasn't fun either.