If your opponent uses a projectile, you can either absorb it or dash through it. Of course there's other stuff that can be done but those are the ones I'll concentrate on for now.
Absorbing a projectile gives you Phalanx Cannon which can be used to break your opponent's pressure and apply your own. BUT your opponent can very well predict when you will use your projectile, just like you did with his. So, if he predicts when you will use it and blocks or dodges it you are back to square one. If he IADs, you are in a bit of trouble.
However, if you dash through your opponent's projectile, you have the upper hand. You are closer to them(as long as you dash forward, of course) and can do with them what you want(as long as it's fast enough). You could dash through a projectile then use 5C > Buster and even if they block, you are in their face.
Unless you are really confident in your use of Phalanx, dashing would be a better choice. But let's not forget that you can fuck with your opponent's mind if you absorb a close-ranged projectile-based attack, like some of Rachel's.