For me, I have rarely seen anyone one here diagnosed with a calcium or magnesium “overabundance” 
Yes there is cal and mag in those. There is also NPK in most nutes, in some ratio or another. But for me using RO water with everything stripped, I ended up with a deficiency by not using either enough, or not using it often enough (like non-nute waterings)
I like to think of it like each one is designed to do its job. You are not adding bloom nutes to maintain calcium. You use cal-mag for that so the bloom nutes can do what they are supposed to.