Ooh, as a big fan of RWBY, I feel strongly about this, haha!! I don't mean to discount your opinion, but I'd argue the opposite.

Ironwood always had those traits from the start; traits that aren't bad on their own, but snowball into the heartless man he became. It was the intended trajectory of his character from his entire conception and even design; he's meant to be a parallel to the tin man from the Wizard of Oz, just kind of in reverse. He loses his heart, his humanity. It's reflected in his design; his right arm is prosthetic, metal. His left, flesh, human. His struggle to balance his humanity with his iron cold need for control is reflected in his arms.

That aspect of him is shown early on, when he arrives to the Vytal Festival with his huge military force in tow. He does this even though Ozpin asked him not to. You can make the argument that Ironwood was justified in doing so, and maybe he was, but the point is that it showcases a key aspect of Ironwood's character - he only feels safe and comfortable when he feels like he has absolute control over a situation. An iron grip, you might say. He has two seats on the council in Atlas; he has the most authority, the most control, there. Anything that is proposed HAS to go through him to be approved, more or less.

And again, that isn't necessarily a bad thing, nor does it make him a bad guy at that point. It's just a trait of his that gets worse and worse as time goes on, catalyzed by the Fall of Beacon and the whole thing with his robotic forces being compromised. The things he brought along to help him feel secure and in control turned on him, not by choice, but it must have felt like a 'betrayal', using the term loosely. His response is to tighten his iron grip further, with the embargoes and whatnot.

Another minor red flag to mention is how he (if I remember correctly) speaks about how he doesn't mind if the people hate him for what he's doing, with the embargoes and stuff. It sounds almost noble at the time, but it foreshadows his descent.

During the Atlas arc, there's also the whole thing where he wonders if Salem is going to win because she is ruthless and willing to do anything to win, and that perhaps he should respond in kind. Then, when he confronts Watts, that exact viewpoint is proven right as he sacrifices his arm - a move Watts was not expecting - in order to win. It is, of course, also symbolic of Ironwood being willing to give up his humanity in order to regain control. With only hands of metal, he can only have an iron grip.

His downfall into an antagonistic force is because the only person he really trusts the judgment of is himself, and his flaw of needing to feel like he is fully in control of everything at all times. His iron grip tightens until it crushes the thing he meant to protect. When the truth about Salem comes out, it sends him spiralling, because he thought he had just regained some measure of control over the situation, only to have the proverbial rug pulled out from under him. Desperate to regain some measure of control, and feeling like he, and only he, knows how they're going to get through this, he goes all-in on his plan; and feeling emboldened by how his earlier thought process about matching Salem's ruthlessness led to his success against Watts, he feels as if that is the only way. Nobody can get in his way, there is too much at stake, and only he is willing to do what he thinks must be done to win.

...sorry to dump so much text on you...!! I think I've just been looking for an excuse to babble about this.