The way I've read into the rule was that it was as much about making sure the writer earned their rank as the character. Weed out the god-modders, if you will. If someone has already shown they can be trusted with a master level character then I don't see why we should stop them making another, sometimes for a character concept it's not ideal to start at Padawan level and given that NFU can start up as powerful as they like, it's a little restricting.
Saying that, sometimes it does pay off to have to grow someone more than intended with training and such. Not that I'd earned Master rank before but if I had the choice then I'd have started my character Samka here out as an upper Knight/lower Master level character as she was originally only intended to serve as an occasional antagonist to others. I decided as I had to start with Padawan, I had to grow her power up a bit and at least get a Knight rank before taking on that role since I wanted her to be a formidable foe but as I started writing her, I found I really enjoyed it more than expected and she's now my main so I'd encourage people to start from the bottom whenever they can because it can really lead to more vivid characters.
I just don't think it should be an enforced rule if the writer is trusted/experienced.