I've avoided saying anything about whether the OP is right about whether their tech lead is an idiot.
The only conclusion about the OP I see is "The poster thinks the tech lead is in idiot partly based on the fact the tech lead doesn't close as many tickets as juniors."
I think that's a simple implication from the OP writing "he is not very productive — our junior engineers are lapping him on tickets closed".
All the rest of my comment is about how an interviewer might likely think if that were said in the manner discussed; it's not about the OP.
1. That the OP doesn't know as much as they think they do about the job of a tech lead. 2. That the OP is jumping to damning conclusions from dubious judgement. 3. That #1 and #2 correlates with being "challenging to work with."
#1-3 are about how the interviewer will likely think if the discussed remark is said in an interview; they are not my conclusions about the OP.
It would have been more accurate if I'd stated that was a risk being taken by the OP in the interview rather than a certainty. Though I expect that would have made the point less clear to most readers.
#3 correlates with #2 (not #1), and this relation is not specific to the OP.
#2 may not be true of the OP, but an interviewer who thinks it based on things said in the interview, is likely to think #3 follows.
This is a risk the OP is advised not to take if they are trying to make a favourable impression.