For the majority of tasks for the majority of people in NA induction is better. Wok cooking is the only one that it makes tricky (not impossible) and your not doing proper wok cooking on basically any NA home gas cooktops anyway. for that you should be using a proper commercial propane burner. If your not doing that the correct pan (one that will hold and spread the heat) and cooktop will be pretty close to gas, unless you want to bash when putting it down I guess.
As for your cast iron maybe use the correctly sized induction element then? It’s cast iron and it doesn’t spread heat well, that’s how it works. You would have the same issue on a resistive element.
Those propane burners are wicked. I still can remember the sounds of when they are turned on and off (Chinese hole in the wall restaurants usually have the kitchen right next to dining).
They make induction cooktops for woks (they are basically slightly bowl shaped), I’m not sure how popular they are in Asia, however.
Compared to $50-150 for a single-burner unit, that's quite a bit. Plus I like the portability, though I'm probably only using the cast iron under the vent hood.
Ikea has the 36" in stock in the US for 950USD, but the 30" would be tolerable at 800 or 700USD if they were available.
As for your cast iron maybe use the correctly sized induction element then? It’s cast iron and it doesn’t spread heat well, that’s how it works. You would have the same issue on a resistive element.