You are perfectly correct on both counts. That is why I really feel the use of an EC meter is misunderstood.

One the issue of adjusting pH, that is also not too necessary. All of the standard nutes are pH buffered, and if you are topping off the rez with fresh water, the pH should stay stable until the nutrients (and their buffering agents) are slowly uptaken by the plant, then you have water out of the ratio of the buffering agents and the pH starts to rise. Time to change the rez and start fresh.