You just gave Tsonga a major! He actually was just the first name that came to my mind, so I would not be able to compile the list of qualities that yourself and then
@Front242 presented. I would add a very good net game (something which I failed to realize at first honestly).
As Front said, the bh was/is a liability, but who knows, with two less surgeries for some reason, or quicker courts in general, and had he won a major early on... could not he developed in to a different player? Yes, I won't stop repeating that I know quite well that those what if scenarios are, to begin with,
unreal. I am only using them, as you already acknowledged, as a way to argue that those guys are bloody good as well. BTW one of the very few top level matches that I watched on spot (being from South America I don't get that many chances) was precisely Federer x Tsonga. For the occasional viewer, for sure their level seems pretty evenly matched.
Or still... (sorry for the long post) Wawrinka. Can someone precisely tell what happened around 2013/2014, that, as we say here on the boards, transformed the guy into "Stanimal"? What is the difference between 2015 Wawrinka and 2012 Wawrinka, if you, say, watch some random matches during the year? Could someone decisively tell "this is the major winner, this is the top 20 guy"? Sometimes it seems that it is just a very small click that makes a hell of a difference.