Shazam is a character with incredible mixup. He isn't supposed to be easy to pick up. This character is very rewarding in that once you do finally get in, the round is pretty much over. You're calling Shazam a bad character not becuase of his faults, but because of yours. Of course superman, deathstroke, and doomsday are easy to pick up. They're also a lot easier to scrub out with, but that doesn't make them better characters in the slightest aside from superman being pretty ridiculous. He has pretty decent range on most of his chains, f12 and b23 being examples of this. J2 beats pretty much everyone air to air in the game, making it an amazing anti air. Plus most characters don't have an AA. You don't need a reversal, if anything, not having one teaches you better mechanics and will make you an overall better player. He does not have a shitty b3, have you seen Adams? Why in the hell would anyone besides Ares and Lantern use f3? He doesn't need a good projectile, the one he has is good enough to trade with other projectiles if you have the life lead, plus he has a teleport. Complaining about inputs being hard really doesn't make him a worse character, I'd use C. Viper as an example but I'm not sure if you know who that is. If they jump back they're pushing themselves into the corner, in which Shazam's mix up is much stronger anyway. And blocking a reversal to punish is part of the risk you take when setting up a vortex, you have to guess as well. Plus you can punish almost every reversal in the game with 22>command grab, or even just a raw command grab.
So there you go. Get into training mode, and practice match ups. You'll get there. You just need to stop blaming the character instead of blaming yourself, and look to improve.