I have stainless steel and anti-stick pans from a high end brand, and with one of the cheapest induction stoves a liter of water boils in literally 2m, compared to 10m+ of gas.

Cast iron pots have additional challenges unless they're designed for induction (flat bottom surface), and even then, due to the high thermal capacity they are basically bad heat conductors, so if you put a large cast iron pot on a small induction coil, the center will heat rapidly, but it'll take a long time for the whole pan to heat up. Your only option is to make sure bottom-pot size and coil size are matching, and even then it'll take a while longer to heat compared to stainless steel or copper.

I did say it's excellent at boiling water, didn't I? Everything else is horrible.

In terms of cast iron, even if I leave it to heat for over 20 minutes, the hot spot is still there.