Alex savage doesn't block anything. Regular coil did. Regular coi was also definitely easier than alex savage. I pugged t13 in df multiple times when it was added; low success rates, but possible with pugs. Get yourself a decent pf group and you were solid.
I mean, would people have really enjoyed t13 if it was as faceroll as normal alex? Different stroke for different folks, but that woulda killed the bahamut storyline if I rolled in same day he was added and just wrecked him in a df pug. Part of what made that story so engaging was that he was a legit big bad. Same for t12, if he was faceroll after those cutscenes it would've felt weird. I still would've enjoyed the fights for the mechanics, but the story would've been less engaging by a lot.
It has nothing to do with exclusivity. I don't mind other people having what I have. I mind other people telling me what I have needs to be lower quality so that they can have it.