The 3rd reason could be a powerful one. But to be honest, those are legendaries to begin with, so pretty slim changes of getting them anyway, especially those specific airdrop legendary cards too. The 2nd reason is important too, but I already have a decent airdrop of SPS. For the potions, I already bought and have more than enough and will still need to buy a lot more packs to use them all. :) I don't know... excitement is too high, lol.
But that was a very good presentation of reasons against, when everyone wants to just open them. Well thought!
It's true that the probability of getting legendaries doesn't change really but I'd prefer to get a legendary summoner rather than a normal legendary card :-)
Anyways, I don't believe that we can prevent ourselves from opening some packs :-)