Yeah, I saw so many posts where people who completed the game 2-3 times complain that "GO-TO is obviously unfinished, since we have never seen the man himself after the yacht". They never found out...
When there is only one available slot for teammates on Onderon, who will choose rather weak and "unfinished" GO-TO (you can make him somewhat useful after manual leveling and equipping him, but other companions will still be better)? And Dantooine, surely GO-TO isn't the first choice when you think about that planet.
The problem, in my opinion, is that there are no situations in the game where the presence of GO-TO in the active party would be more beneficial for the player than the presence of other team members.
I can only name 2 moments when I wanted GO-TO in my active party and both of them from M4-78 mods:
1.The original M4-78 Mod mostly consists of fights with endless swarms of droids. I vaguely remember one diffucult fight where strong spider-droids with shields from Kotor I and a bunch of others just surrounded my party from all sides. Using GO-TO's ability "Manipulate droid" there can be pretty fun and useful.
2. In the M4-78 EP 1.2 at the beginning of the planet player must use one of the droids, and each droid has unique sidequest. So we have a reason to try GO-TO there (reminds me of Leviathan from Kotor I).