The new FBiOS the government wants to compel Apple to write would have an unlimited number of password guesses, no delay between password guesses, and an interface to accept passwords entered automatically through a data port instead of manually through the touchscreen. This combination of security loopholes would enable anyone to break into the phone in a few seconds. This most certainly is a backdoor.
There's a few things wrong with what you've said here. First of all FBIOS is a piece of propaganda dreamed up by Apple. Tim Cook also called it "CANCER" for phones. That is just spin.
Second of all, the combination of security loopholes would not break into the phone in a few seconds unless the password were extremely simple. I've read it would take as much as a year (at maximum possible speed) if the password is six digits long alphanumeric.
And thirdly, a "Backdoor" is generally regarded as a covert security hole unknown to the clientele or manufacturer. Seeing as everyone knows about this incident, it fails the "hidden" aspect of "back door", and since it would be installed officially by the company and deliberately created by their team of software engineers, it would accurately be regarded as a new "front door."
:)