What part of RFA don't you understand? GS could've (and almost certainly would've) matched any offer the Spurs threw at him. There was never a remotely realistic chance that they could land Draymond. If you want to argue that Draymond is better than LMA and that he fits SA better, that's fine. I even agree with you. But arguing that the Spurs should've pursued Draymond instead of Aldridge is beyond stupid and a different argument entirely.
Aldridge hasn't played up to his contract so far, but:
1) He's steadily improved as the season has gone on, and there's a good chance he'll continue to do so as he gets more accustomed to playing here
2) He hasn't been nearly as bad as you're making him out to be
If he's still playing like come April and is a no-show in the playoffs, fine, criticize the move all you want. But doing so now (when anyone with half a brain could've told you he'd likely have some growing pains as he struggles to adjust to a new playing style), and to the extent you're showing, is just ridiculous.