Fair comment to take local conditions into the consideration. Then again I'm not sure how many spots would fit that description. And how many of those beginners would learn on. Seems to be more of the exception. And here we got quite a lot of gust at times ourselves - with spots inside a fjord.
As for the sizing. I agree that too big also got a downside as you might get lazy with your technique with time, but that is to me the lesser evil compared to not even getting up to ride. I know as someone being big how it feels when a instructor gives you a kite that is too small. It is safer for them, but it means water start after water start. Not sure how that is good for anything really. As you at least get somewhat going I agree challenging yourself to hone your technique being underpowered or riding in difficult conditions can only be a good thing (as long as you can safely master them).
Both extremely wouldn't work. Going out as a beginner with a 17m in 25 knots I difficult conditions means disaster. Going out in 13 knots on a 12m means you are never getting out of the water.