FWIW, my cooling system has never been apart in 100K miles/seven years. I have never done a flush and my system looks brand new.
My process is to open the radiator drain **** annually (cold) and let it drain out slowly overnight (leaving the overflow tank cap off as well). I usually do this after changing the oil.
Then refill equivalent to the drained amount (I measure it) the next morning, using fresh coolant/water mixture. My cooling system looks brand new, as I never let the coolant and additives deplete, nor do I chemically shock it by using a harsh flush chemical (typically hydrazine - N2H4 - think about it), or by having a huge delta between the old and the new coolant solutions.
This is based on my experience with 'other' coolant chemistry, and it has served me well for several cars over the last two decades. I have never had a cooling system failure since going to this method, plus it is easy and cheap.
Just my .02