Generally, I have better luck with a temp setting than a power setting for a slow cook, but I'm also over 5000 ft elevation so my boil and simmer points are probably shifted from yours. 180 does a pretty good job with a braise for poultry. For some beef or pork cuts where I'm shooting for a higher internal temp than 180, 210 usually works pretty well for the latter half of the cooking in those cases, and use 180 for the first half.
You should understand how the temp setting works. Under the glass is a temperature sensor. The glass only gets hot from what the pot radiates back to it as the induction heats the metal of the pot. So it's a fair approximation of the temp of the pot bottom. The unit polls the sensor at set intervals. If the temp is lower than you've set, it turns on and runs some cycles until the sensor exceeds the heat temp setting. And repeats.
With a large pot and a lot of stuff in it, 210 usually cycles to a brief boil and then shuts simmers from it's own contained heat for a few minutes and repeats. Remember, water boils at 202 at my elevation so the pot bottom is getting hotter than 210 on a heating cycle, it just can't conduct the heat into the pot as fast as the induction coils add it. It's even enough heat overall. 500 watts gives me a continuous boil usually, but it can be slow to get there.
Cast iron is not my favorite choice for induction. It tends to be much warmer over the induction coils and much cooler away from them. With liquids, it should even out enough to not matter. But if you try to brown a few cutlets in a 12" cast iron pan, you'll see it's not an ideal match for these induction units. They have induction coils in about a 6 inch circle. Works Ok on a 10" cast iron skillet, but not a 12. I've had pretty good luck with disk and clad pans though you can see some of the same behavior there too. But the conductive aluminum core helps even it out better than cast iron can.