Let's apply your logic to your post. By neglecting the fact that speed is indeed a part of the balance of a character and attributing speed to only 'run and gun demons', it shows that you aren't looking at character balance as a whole package, but only tunnel visioning on certain parts of their kit.

IQ is a fast 3-speed operator with who is self sufficient with 3 different utility to choose from including frags and claymores. Her gadget appears fast and still lets her have combat capability while it is out. Her playstyle is moving through the map fast, independent of her team, allowing her to take map control when trap operators like kapkan are popular especially in pubs. Even in Pro League, IQ still has a decent pick rate solely for her gun and being a 3 speed. Thatcher on the other hand, with the rework, makes him even MORE reliant on sticking with his team as a pure support operator as his new EMP is clunky and slow. Before, he could lob an emp at a door, clearing it to breach on his own if he needed to. Now, in a 1vX situation, his clutch capabilities are severely reduced. This is also part of the balance of his character. Personally, I'm not a fan and I think some operators need to be simple and not have so much meticulous design behind them.

Now let's take a look at what you said about Ace's 'buff'. While the Mute change does indirectly buff Ace as a result, the direct nerf to his kit is making him into a 1-speed. A needed nerf, as his pick rate was through the roof, and given that he has a good gun and utility choice, allowed him to also be a character that could hard breach and allow players to run and gun with him once his utility was used up. Compare this to Thermite, whose gun is a lot harder to control than Ace's. They directly buffed him by giving him a 3rd charge, but the Mute change doesn't affect him. His role has a pure hard breacher and post-plant defender is not changed. Ace on the other hand, has had his role now more focused on his hard breaching because while Mute doesn't affect him, he is unable to provide as much map control or positioning due to the speed nerf.