They'll probably help. The top tier is being dragged down, some of the super bads are going to be good now. I don't really see this as just a shuffle of the tiers though. The characters that are going to be the best probably won't be the best by an obvious and ridiculous margine like they were before. So, it will probably help the game.
Regarding Mileena, she is definitely better. But she still has some very wonky things that make her less good than the other beneficiaries of the low tier steroids.
The good - her IAS having less recovery is huge. She can now combo a raw IAS as an air to air into a roll for a follow up juggle. Her low sai being more plus is also huge. Her D1 seems to be less broken from point blank range. Buffed D1 and D3 actually give her an option to get out of pressure that doesn't leave her -1435824895178947892345. B12 remains great. Less recovery on sais also means that she can bait out jumps and punish them on reaction with TK, so telekick is no longer totally worthless.
The bad - F3 is still garbage, you can catch people sleeping, but it seems to only actually work once per set if that. Being a low crush isn't that big of a deal. Lack of viability of that overhead makes F4 pretty bad as well, since it doesn't really need to be respected that much. EX TK and regular TK into air sai are still super inconsistent. EX TK can still wiff on hit sometimes. Roll and EX roll leave you at weird and inconsistent distances from your opponent on hit. Sometimes you're close enough to follow up with B34, sometimes you are too far and need to NJP, sometimes you're too far to connect with either and you can't follow up with anything. In the last situation, you just used a -54821390402184943 roll as a very high risk vs reward move, and didn't get the reward you should have. Her BnBs depend on how far the game decides it puts you after you've connected a roll. Sometimes you can't even use them.
Scorpion - The F2 change is not going to make his S tier. The 2nd hit of F2 and the 1st hit being cancelled into a low can be fuzzied. Always.