It’s not that he doubts the Tsaritsa’s judgement— he’s sure she’s picked the individuals best suited to accomplish her goals; but if you are what’s considered capable enough, he’s mildly concerned about the quality of the rest of the Fatui’s recruits.
The prospect of promotion is something of elusive nature for humble subordinates of the Harbingers, a carrot dangling in front of a donkey long-given up, and as duplicitous as the Tsaritsa can be in her ambitions, he highly doubts that a regular Cicin Mage like yourself has what it takes to be her attendant.
Her closest confidant. Her most trusted advisor. Tartaglia doesn’t think anyone could be worthy of such an honor.
“I don’t understand what the Tsaritsa sees in you,” Tartaglia tells you this, and you smile mildly, a smile of no real significance or associated emotion.
It annoys him.