Setting aside that these are effectively tweaked immortals, the main selling point SDS used for signatures was the increase in lineup/roster diversity because there will be more signatures than there were immortals. Based on what we have seen so far, this is likely to be an illusion for several reasons. First, the XP progression is going to give everyone the same 5 (assuming you get to 100 diamond) likely inferior signatures (because they aren't all created equal). Second, the ones they drop in WS/BR will be extremely limited in both numbers and availability (to the point that they will have virtually no impact on roster diversity), especially if the meta develops in a way that certain cards become obvious choices (thus making the say other 2 options in WS virtually non-existent). Third, everyone will get the ones they likely have in the moments programs (assuming at least a few are in there). About the only real diversity will come from the ones they release in the innings programs and again that is only if they are able to keep the meta balanced.
I think a far better way to release these into the game (assuming that lineup diversity was their goal) would have been to hold most for the inning programs (maybe even having a choice of 5 vs 3), give WS a set one each month (vs a choice pack), and then have 1 set for BR where you only have a chance to get it with a perfect run otherwise you get 1 of 5 "regular" BR cards (this would make that sig very sought after, but also give repeat BR winners a better shot at getting it). The way it seems SDS set these up is that most of these signatures will be in such quantities as to make them have almost no impact on diversity even if the meta is balanced.
I think we also need to see how the game freaking plays guy. Making all these assumptions and games not out for another 11 days. First off, according to Ramone, defense does mean something this year and with increased pitch speeds a very good defensive/pitching team may actually be able to combat an all power team, so a guy like Brooks Robinson SS may be far more useful at 3B then a Chipper Jones. WE have to wait and see at launch and next weeks tourney will help to.