1) Is the number of completions set to high, or is it just right?
2) Do you feel it's meant to have players specialize in only a few characters, or to keep players who want to complete them all playing the game for the long run?
3) Should they adjust the amount needed (ex. 100 Operations Completed), or should they just alter the challenge (ex. 250 zones completed)?
Me personally, I think 250 operations was a pretty steep number to begin with. Even if you got a rhythm going and can complete a game in 7 minutes, that's still 30 hours per agent (and with 15 agents that makes 450 total). I would have preferred if - when the game released - it was 250 Zones completed. As of now, I don't really see any point in changing it.
I have completed all of the older characters with the exception of the Necromancer, I have 170 completed runs with her. Each character by the I finished 250 runs I was incredibly familiar with the variety of builds that I enjoyed the runs. I did up to 100s with all before running for the 250's. Early ones done routine/threatening/perilous, later threatening/perilous and more recently perilous/NM. now it is 2 runs in perilous and then 2 runs in NM so promote more frequently.
Having said that if you want the banner, you do the 250 runs, if you don't care to do that many runs so be it no one will be forcing you. If you want promotes then do it at higher difficulties.
Now I am working on finishing the Necro banner and also the Avvar and Duelist 250 runs, they are at 110 and 70 runs, Virtuoso is at 12 because I don't care much for him. Once done I plan to play whoever catches my fancy. These challenges allow you to play the character thoroughly in various builds and modes, and if do it stages, it would help from being a complete monotony.