I agree with most of this. However, I would disagree with the idea that the command grab should stay as is. Changing the command grab into a mid special would give him access to a d1 special that requires meter to extend into a full combo. Just about every character in the game has that, so it's not overpowered.
Yes, it would also give him access to meterless damage in the corner when used in conjunction with the clone, but thats ok for two reasons. Number 1, he wont be able to put up clone and use plus frames due to the fact that his plus frames cpme from ex db1 (which will shatter the clone) or clone toss. The only other plus frames he can get on block is off his f3 or b3 (which is universal) Secondly, meterless damage in the corner using the clone is a far cry from meterless damge other characters get from specials and launching normals they have. Black Adam black magic, Harley tantrum stance, Atro with dex, hell Superman's f23. So, Sub needing to have the opponent in the corner, land a hit, and hit confirm into the special, while the clone is active, is NOT overpowered.
Lastly I would add that his iceball is too slow. The normal one is a 25 frame start up high that moves slow asf. Making it a basically useless projectile. The meterburn version is just as slow, making it incredibly difficult to use in counter zoning because of getting hit out of the start up and opponents being able to easily recover before the slow moving projectile reaches them. Solution: Normal iceball start up frames reduced to 17. This is the same start up as green lanterns projectile. However, the projectile itself will still travel slower. This, by default will make his meterburn versions start up faster. Next, SLIGHTLY increase the travel speed of the meterburn iceball.
Mkx subs iceball was slow, but the trade off was it would freeze on trade. Now that it doesn't freeze, its just simply the worst projectile in the game by far. And the mkx sub ex iceball start up was faster due to it being a ex move instead of a meterburn move. They didn't so anything to compensate the character for the changes necessary for him to work in Injustice 2.