It's unfortunate, because I just don't think Ant-Man is the vehicle you want to introduce Kang with.
spoilering for length, and for off topic musings:
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From the start, Ant-Man, like the Spider-Man films, were the more light-hearted in tone films of the MCU compared to many of the others (before Ragnarok revamped Thor's character into a more humorous take. I think Ant-Man, Guardians, and Spider-Man aren't the franchises to introduce Kang with.
I feel like Kang would have been a good character to introduce in a Doctor Strange sequel prior to Multiverse of Madness, while still leading into MoM.
I don't think Kang has to 100% be true to the comics version, and even with Thanos they took creative liberties, so I probably would have done something like this:
I'd set it between Wanda Vision, Loki Season 1, and Multiverse of Madness (so, it'd be WV, Loki, Doctor Strange 2 w/Kang, No Way Home, Multiverse of Madness, and a Kang D+ series I'll get to below). Have Kang debut in this new Doctor Strange 2, and perhaps he gets bested by Strange (at least Strange is a demonstrably very powerful hero compared to Ant-Man) or incapacitated in some way. After this loss, he sets off on a journey of revenge, traveling the multi-verse, wiping out or subjugating alternate/rival Kangs, while also killing any Avengers from those universes that get in his way, and, Highlander style, he is getting more and more powerful the more multi-verses he traverses and Kangs/Avengers he destroys, leading to him eventually coming back to "our" MCU, where he confronts the latest roster of Avengers in Avengers 5 or whatever.
I'd even do a limited series Kang D+ show (like 4-6 episodes), where, to separate him from Thanos, I'd do a more "fall from grace" style story. He starts off with good intentions (similar to some of the variants we see in the Loki series), but his defeat by Strange breaks him. It'd lead into Loki Season 2, and Doctor Strange: Multiverse of Madness (now Doctor Strange 3), and while I wouldn't have him be the villain in MoM (I'd keep it as is, as a follow up on the Wanda Vision stuff), but have a stinger at the end where we see where this new Kang is at in his quest to rule or kill the other Kangs, and we get a similar look at the council of Kangs we got in Quantumania, with this new Kang arriving to take over, with his army of subjugated Kangs.
I think it'd make him relatively different from Thanos from a characterization standpoint, give him at least a little pathos by painting him as a fallen "hero" (in his eyes), and sets up why he'd take umbrage with any Avengers he encounters while traversing the multi-verse. And, since Tony Stark is dead, we can now shift the blame to it being all Doctor Strange's fault. lol. Let Strange be part of the catalyst that puts this Earth in Kang's sights along with the events of Loki Seasons 1 and 2.
We could have even included a little Kang teaser in No Way Home's ending stingers (since it happens before Multi-verse of Madness), where Kang targeting "our" MCU again is reinforced because of what Strange/Peter did in No Way Home, further fracturing the multi-verse, and making Kang's desire to control/rule the multi-verse stronger because clearly Strange and these Avengers have no idea what they're messing with.
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On topic, I really like Michael Douglas and Hank, but I also wouldn't have minded if they went along with his wishes to kill him off. Even with Spidey being a more light hearted series, they didn't shy away from killing off major characters, so it could work for Ant-Man too, I'm sure.
I don't think it seems like he wanted out because he didn't like playing the role, just that, well, he's not as young as he used to be, and knowing that these Marvel movies are this long, intertwined narrative, he's probably thinking about how much energy he wants to devote to these types of films/characters in the long term. I'd have hated to see Hank die, but then again, that's kind of the dramatic point, right?
They could have done potentially the inverse of Janet's sacrifice to save thousands of lives that led to her being lost in the Quantum Realm, and have Hank do something similar, where he sacrifices himself to save Janet, Hope, Scott, Cassie, and the world, but unlike Janet, he doesn't get lost in the Quantum Realm, he actually dies. And since Douglas wanted an epic send off, that could be just that, and a sweet mirror to Janet's sacrifice. Hope gets her mom back, Hank gets his wife back, but it was short lived, and now Hope loses her dad, and Janet her husband.
variety.com
