The term "junior" itself has certain negative connotations. Among the various dictionary entries we have, for example: adj. Low in rank; having a subordinate

The term "junior" itself has certain negative connotations. Among the various dictionary entries we have, for example: adj. Low in rank; having a subordinate role, job, or situation. n. One of less experience or inferior standing in his profession than another, who is called his senior; one employed as the subordinate of another, especially at the bar. n. term of address for a disrespectful and annoying male I'm cherry-picking these, of course (out of a body of mostly neutral variants), but the point is, these negative touches do carry across. "Senior" is a bit different, somehow (mostly because it's no intrinsically defined in terms of negative attributes like "inexperienced" or "subordinate").