Alright. Time to break it down.
All of the changes to Sc5, from previous iterations, was done to combat SC's turtlish nature. In comparison to previous SC's, this one is a breath of fresh air. It's faster paced, more exciting, and you can't expect to out-turtle you opponent. High level play of sc2, sc3, and sc4, was a game of turtling, poking, footsies, equating to a boring game (at least at the high level). Sc5 pretty much solves all those problems.
To be fair, sc5 is not a "perfect" game. No fighting game in the history of video games can claim to be balanced. Although, despite sc5 having glaring imbalances, it's still a hell of a lot more balanced that sc3, or sc4. Sc2 probably had the best balance of all, but the game had flaws that I personally could not overlook.
As for "stuns", my suggestion (if you still give a shit about sc5) is to look up frame data for your mains, as well as all the characters that give you trouble, and figure out when you can sneak in a quick move for Counter damage. Some stuns can be shaken out of, although more of them were shakable in sc4, that much is true
For example, if a move says that it's -20 frames on block, that means you can punish them with anything that is 19 frames or less on impact speed. If your attack is 20 frames, your weapon will clash with the opponent leaving you both at neutral. Once you get the hang of that, the game as a whole becomes ten million times more rewarding. The more you understand SC, the more fun it is.
Everything in SC involves some risk. That's what makes this game so interesting. You can't just spam attacks over and over and expect not to be countered. Everything can be trumped by something else.
As for inputting commands, this game feels no different than any other SC in terms of how sloppy you can be and still pull it off. Tekken has MUCH stricter inputs.
One of the drawbacks of having the quick step mechanic is that double tap, side stepping moves (22_88 commands), now are 10 frames slower than they used to be, because quick step is 10 frames. It doesn't really bother me that much, honestly. It's a fair trade-off for having the ability to step really fast.
As for "supers" being broken, no their not. First of all, they are not "instant", second, the fact that it requires a whole bar of meter balances this out. If your opponent has at least 1 bar, you should expect them to throw it out, and be ready for it. I don't know if you have noticed this, but a CE does a lot less damage when it's at the tail end of a combo.
And finally, I agree with you that wall combo's need to be nerfed. There needs to be a massive damage scaling down as each attack connects. It wasn't that crazy in previous SC's, that much is true. But, compared to all of the massive improvements in just about every way imaginable, I can look past this. Here's one solution to this: avoid getting your back to the wall as best as you can. I understand that sometimes it's unavoidable, but do whatever you can to keep your back away from that wall. It's similar with ring outs: I avoid the edge of the ring no matter what, even if I think there's a good chance I can ring them out, there's also I chance that I can be rung out as well. The only time I may go all-out for a ring out is when I have a very little health and my opponent is practically untouched, when I basically have nothing to lose and I've pretty much lost that round anyway.
I am gonna be dead honest with you. At first, I hated sc5. I mean I REALLY hated it. I hated the supers, hated that they changed GI, hated JG, hated the insane damage output for everyone, and hated the meter concept in general. The more I played it, the more I liked it. Now I absolutely LOVE this game! One by one, all of my doubts disappeared. I had to play the game for many hours before I started appreciating all of the changes.
Like it or not, this is the direction that SC is going in. But based on what you said, it sounds like SC isn't your cup of tea, whether it's sc5 or any previous SC, because many of your complaints were things that have existed in SC for a long time. Not do be an ass or anything, but either you should put up with it and learn to like it, or stop playing SC altogether and play something that you consider is a good game.