I guess in my case I have a very hard timing filling that blank slate since I usually play a lawful evil persuasion character. I still don't see a reason why I should care about the thieflings but I don't see a motivation to wipe them out either. What's in it for me? A basket with food? Seriously? The goblin part idem, I need motivation to slaughter them all but since I'm evil there isn't one. And killing just for killing is 'stupid evil' in my book. So after playing EA I still have a blank slate. This was with a high elf rogue. The lolth drow cleric is getting a little more feedback from conversations and doesn't start as a Baldurian so that's good. Still I haven't reached the grove yet but I suspect I will hit the same problem there with her.
Edit: also the tadpole part. I didn't use it, doesn't seem very safe to me. I can't trust it, it might even turn me into a mindflayer. So that's even less blank slate content filled. The companions also get the tadpole convo's so once again companions are outdoing me.
you've filled out that blank slate more then you evidently realize. Your character is motivated by personal gain, what he can get for doing what an npc wants. (hence he's greedy, or selfish), he is more of a friend to evil characters cause he is one. (hence he's more neutral, so far because he doesn't really care about good evil, or right or wrong. It's about him. Lawful neutral is looking more likely) He also has a firm belief that killing just for killing is stupid evil. (again more neutral then evil, since theres nothing in it for him, and it's just stupid for killing randomly, and indiscriminately) He is in part a rebel probably kicked out of a High Elf community do to his 'Evil' ways, vs his peoples 'good' ways. If he was part of one to begin with. He goes against the grain of High Elves being magic users, in the fact he is a rogue quick of tongue, who wants others to see his point of view with words, other then a knife in the back. So he's probably charming (or thinks he is), yet oddly enough those around him may very well find him charming (alot of persusion checks passed) or find him annoying (alot of checks failed.) or some where in the middle.
So simply by doing what you did, you filled out the slate, and never realized it.
as a writer (or wannabe) I can tell you truthfully, that even the characters we right get away from us, the take on a life of their own without us even realizing it. Some try desperately to keep a character true to the idea we formed them from, yet still escape. Indeed many characters are not who they were when we first thought them up, or become more important then we ever thought they'd be. An example is Drizzt (who some hate, some love, and some don't care about) he was meant to be a secondary character, yet as Salvator wrote he took on a life of his own, and become the (star) of the series.
edit (quick note) Everything you stated is what the creators of those companions did to create the companion. It's not that your pc is outdone, it's the fact that the companions had more time to be fully fleshed out.