Wade knew this was a possibility but he chose to opt in. He wants his money.
I don't think it is petty to play out the majority of the year. They should keep him until and if they get a good enough offer that it benefits them to partially buy him out.
Oh there's no doubt that Wade knew what was coming and he intentionally opted in early, before the Butler trade, so that he could say he thought the Bulls were going to be contending next year and wouldn't have opted in otherwise and use that for his reason for wanting the buyout right away. He wants the full amount, the Bulls don't want to pay him to just go play with LeBron. They deserve to be stuck with each other.