I thought Jonas was just a replacement for Daniel. I mean, in Meridian he was a parrot of the government until he suddenly developed a conscience, then he suddenly develops a kind of superbrain to catch up to Earth's level of knowledge and now he parrots Daniel's notes or comes up with the sort of "How stupid the rest of SG-1 are that they didn't come up with that" ideas.
He could have been an interesting character, like the one from New Ground who returned with SG-1 (could have been), but as a regular? No thanks.