The difference is that Banner works to maintain his rage, while Ultron's drives him to trigger an extinction level event.

Source: https://collider.com/ultron-origins-mcu-marvel-comics/

The fact that he's played by also helps - though took Ultron's casting in the different direction.

Source: https://collider.com/ultron-origins-mcu-marvel-comics/

Things went a step further during the "Ultron Unlimited" storyline, when it was revealed that Pym had based Ultron's brain patterns on his own - and since Pym was dealing with mental health issues, he may as well have passed them onto his "son".

Source: https://collider.com/ultron-origins-mcu-marvel-comics/

While Rhodey has fought Ultron's android soldiers and the alien forces serving Thanos, he has no prior experience with the villains of : Skrulls.

Source: https://www.cbr.com/secret-invasion-nick-fury-war-machine-adversary/