All things being equal…all things are equal. Granted. But, that’s not what the OP is asking about.
The control in our experiment would not be the amount of heat a method of cooking procudes, but the food that we’re using. If we were examining wether Mercola’s evil microwaves degrade food, then, yes, we would submit the experiment per your assertion. But, we’re talking about cooking the food via two different methods of cooking. If 1) boiling, steaming and microwaving heated the food to the same temperature as a matter of course and 2) the amount of time is the same for each method of cooking, you are correct.
According to: Food: Recipes, Cooking Tips, Celebrity Chef Ideas & Food News - TODAY.com | TODAY we cook the artichoke for two significantly different times for microwaving and steaming (5-7 vs. 40 minutes). Assuming that the food is the same quality (tenderness, etc.) afterwards, I think it’s safe to say that the microwave heats the food a) faster and b) hotter. I’m not suggesting that either the microwave heats the food 8x hotter, nor that we could cook the artichokes in one minute if we used a method of cooking 5x hotter than the microwave. Check out the following cite:
According to: http://www.co.st-louis.mo.us/doh/FoodCenter/final_temps_factsheet.html
Yes, the rest of the page is about toxins and etc., however this section references evenly cooked foods, which I’m assuming we’d want if we’re eating them. LA County Department of Public Health agrees with the 25* rule.
More heat = more degredation of nutrients. We’ve agreed to that. Now: microwaving to cook food to generally accepted standards of evenly-cookedness = cooking food 25*F higher than “conventional” (read: non-microwave) cooking = more nutrient degredation.
Before you argue that the longer time that the artichokes spend in the steamer, the longer they are exposed to the maybe/maybe not same level of heat, the longer the nutrients have to degrade, let me mention that my Countrys Delight Sweet Peas and Carrots directs one to use the same amount of time to cook via both boiling and microwaving. It says nothing of steaming, but if our microwave uses 25% more power, then I think we’re in the same situation where more heat = more degredation.
I addressed this above.