St. Mary's this year has taken less than 10% of their shots from mid-range. Over 90% of their shots have either been 3s or at the rim, yet they have one of the best offenses in the country. Has forgoing the mid-range shot hurt them more than it has helped them? They have been taking an incredibly low number of mid-range shots for years, and yet their offense is consistently very efficient.
Four teams which consistently take very few mid-range shots are St. Mary's, Davidson, Belmont and Iona. These teams all are known for having very efficient offenses (defense on the other hand is not always a strong suit for these teams), minimizing the number of mid-range shots they take has not had a net negative effect on their offenses. They have been taking very few mid-range jumpers year after year, yet they always have very efficient offenses.
In general, the size of any negative effect of reducing the number of mid-range shots (like your hypothesis of defensive adjustments) is tiny in comparison to the increase in efficiency when the mid range shot is deemphasized. Now, no coach is going to completely disallow mid range jumpers, sometimes that is the best shot a team can find in a given possession and it should be taken. However, I don't think coaches should draw up plays where the goal is to get a good mid range jumper. That should always be the last option.