So what we should be looking at is the median number of tenures, not the median length of tenures? How would one weight the latter by the former to get a more robust measure of tenure length?
Well, what do you want to ascertain? In any case you won’t capture the long tail of long tenures, because you don’t know how long current tenures will extend into the future. What you could measure is the median current seniority of tech employees (how long they are in their current job), which would be a lower bound for the median of (eventual) tenures of current employments.