However their VUs are still far away,which is why they get these texture rebalances,it is possible that pantheon will get a VU of some sort in the near future(like after kassadin or after ryze who are the next on the list for a model-update and a full vu).
Kassadin,Sion,Tristana,Alistar and so on never received a texture rebalance because their Visual updates were close to being finished.
If you want to know which champs didn't receive a TR yet,check this thread out,I keep track of all the visual updates and list all champs who were released before the ashe VU(basically the newest model to ever receive a TR) and didn't get any sort of update to their model since then
http://boards.na.leagueoflegends.com/en/c/story-art/uA3sReav-so-what-can-the-texture-rebalances-tell-us-about-future-updates