Even if Madden ratings were 100% indicative of the actual real to life player, that still is not enough to compare it to a real life player.
There are a ton of factors in real life that are not a part of Madden going into it, aside from the intangibles (which are the biggest factors) there are things like actual awareness (I know this is a rating, but IMO it is impossible to replicate and is, more often then not, a guessing game (what does it mean anyway?)), intelligence (relative to the QB position), and just overall ability.
And not to seem rude, but I think your answer is a cop out.
We all want the ratings at the end of the day to be as close to real life as possible, and by in large, I think they do an excellent job.
But all they have to go off of is what we see in games. It is really a big guestimation that they have to go through.
How many times through the years have you seen an addition Madden rating be so bad on the high end or the low end it was laughable? I don't know how many years you have been playing Madden, but before there was such a thing as roster updates, this was an extremely regular occurrence. I am sure you can go back at the original ratings from last year and find probably 2 or 3 dozen that are incredibly far off. We have already seen it this year with players.
So yes, as much as we want to believe the ratings are good, and for the most part they are, it is foolish to compare player ratings in Madden to a real life competition.