About the Event Gacha box, the special SR odds are even worse than the description makes it sound. I've done 10 draws on it (picked up the intro special at the beginning of the game which came with 7 + 3 on top of that) and obtained 2 non-event exclusive SRs from it, one of which was double that I owned. On the 5th draw it will be a 100% chance of an SR to be among the 6 cards, but that SR can be any of the 17 included in the pool. And of the pool of cards over half of them are regular SRs that have been around since the beginning.

Once you draw an SR, that one will be removed from pool which will now consist of the 16 remaining. So if you go through the 5 steps again you'll get another 100% chance of an SR which could now be any of the 16 remaining, half which are still regular ones we've always had access to. So unless you're feeling super lucky or want to throw a ton of money at it, the Event Box is a pretty big rip off in my opinion.