(Don't yell at me too badly)...
There are smart people (e.g, Ben Taylor of thinking Basketball) who have KG above TD all time as a player in their prime, as his mobility on defense was better (not as good at the rim), he was a better shooter in general (though, not as good of a post player). There are things that KG was better than Tim at, and if they played in the current era of pace and space, and you anticipate a movement of KG out to the 3 point line rather than his 20 foot jumpers, I'd rather have KG over Tim.
I have TD above (primacy of rim protection, willingness to play as a 5 so the Spurs could access the lineups with Horry / Bonner which were +/- monsters), but I don't think it's outlandish to think KG was better as a player.
A lot of the difference comes down to accomplishments, and soft things like Tim's ability to mold his game over time and fit into different offensive roles, and adapt as a leader that kept the team together. Those leadership skills / intangibles are incredibly valuable as a franchise player.