i dont think the franchise mode was anymore "broken" than the gamplay (as in not so). do most/all franchise modes have some problems? of course. but even 2K5 had many people developing "house rules" as you put it for
gameplay to avoid exploiting AI issues. just search "house rules" here @ OS to see proof of this.
yes there are things like:
-problems w/ CPU signings (too many good players @ the same pos or none at others)
-draft class bug in the 1st round
-trade exploitation
-progression issues (too fast, no one goes backwards, the different attributes which improve dont always naturally "mix" or go together)
this doesnt equate w/ broken for me, however. even the amazing gameplay of 2K5 has many more issues than this (some of which can be corrected w/ sliders or house rules, & many which cannot). but nobody would say the gameplay is "broken." it's amazing in spite of issues-- & all sports games will have some issues replicating reality.
i love franchise mode in 2K5 & many other games despite a few issues. do i play more than 2 seasons like you said? almost never, but that isn't because of any deficiencies in the game mode itself... it's just because i that's how i like to play franchise. personally, i dont think that says anything significant about the quality of the franchise mode.