It has an extremely large downside which is that it opens you up to getting both characters happy birthdayed if you're not careful. I've seen far more people get both characters blown up in a Soul Storm than I have seen make a comeback because of it.
Soul Stone seems like one of the most honest and balanced stones in the game atm. If anything I think its surge effect could stand to be buffed a little bit.
Nah, that's not a downside. Getting comboed during your own infinity storm has the same result across all stones. Soul stone has huge problems with its risk/reward mechanic.
It has all these problems:
-It's currently the only stone in the game which gives you a benefits outside of storm
-Not only the above but it's the only stone which rewards you for doing nothing but activating it (except mind stone, but lol mind stone)
-It drastically improves your mixup potential
-Makes it significantly harder for your opponent to punish your pressure. As even if one of your characters gets punished, the other can break you out of your opponent's combo.
-Increases your damage during storm
-Increases your lockdown capability
-Pretty much negates your opponent's pressure since you can just have one character block and the other attack
Soul stone is secretly the best stone with space a close second. It's pretty much Time, Power, and Reality all rolled up into one in terms of usability. Not only that but it restores your neutral since you can tag again afterwards, and that's massively important in this game.
Let's just get rid of the Infinity stone mechanic completely while we're at it!
But seriously Soul isn't any better than Space or Reality.
Or, I guess, it's definitely better than Reality now...
Nice hyperbole.