Personally, I think if you have a HbA1c of 5.7, and achieve it without lots of hypos, you are doing really (x many) well, and should be congratulated by your Dr.
If you have a HbA1C of 5.7, but have lots of hypos, then yes, possibly you could afford to increase your average BG slightly, if it allowed you more stability.
I think that some Drs (understandably) fail to pick up that we are all different, and depending on lifestyle, what you do during you time etc means that some people can achieve such fantastic results. I got a HcA1C of 5. (something) once, but it was atthe expense of quality of life due to frequent hypos...but if you can do it without, I am very jealous and you have my admiration.