Macbook Pro Wi-Fi problems after Yosemite 10.10.5 update
Jeez, those ping results are terrible.

I'm on El Capitan now, but I can relate to your frustrations about the wifi. My macbook pro is a late 2012 model. I travel with my laptop and rely on it as my phone. It was a real show stopper when wifi would completely bork on the road as in not letting me connect to open SSIDs.

I made this extreme script to wipe out wifi settings and it worked for me, but it is a pain to re-enter ssid/passwords etc and for some reason the problem would show up every now and then. 

For me, if wi-fi doesn't work what's the point of having a keychain? I just wanted it to work, so I was willing to wipe things out to make it so. Mac OSX will create new clandestine defaults, but obviously if you want your passwords to friend's wifi etc, backup your keychain.

You can try the script but be warned, it may not fix your problem, it may even make things worse. I do not accept responsibility for use of this script. Please look at the files and directories it is deleting.

Alternately copy and paste everything but the "#!/bin/sh" bit and run it in a terminal, I have it in script form because it was a recurring issue for me on Yosemite, the problem went away when I either upgraded or clean installed Mavericks (can't remember which I did), so I would consider upgrading your OS to Mavericks possibly. El Capitan is still painful right now with bugs and so on, but at least wifi works.

#!/bin/sh
cd /Library/Preferences/SystemConfiguration
rm com.apple.accounts.exists.plist 
rm com.apple.airport.preferences.plist
rm com.apple.captive.probe.plist
rm com.apple.network.eapolclient.configuration.plist
rm com.apple.smb.server.plist
rm NetworkInterfaces.plist
rm preferences.plist