Yes, this is absolutely the correct metric. For instance, nuts are touted as a high protein food but from a calorie perspective they are often worse than bread

Yes, this is absolutely the correct metric. For instance, nuts are touted as a high protein food but from a calorie perspective they are often worse than bread - 15% of calories from almonds are protein, compared to ~20% in many breads. Lentils and beans are also touted as a high protein source but are only ~20% protein by calories. Compared that to non-fat Greek yogurt (70-80% protein) or tofu (~50% protein). A good rule of thumb for finding high protein foods is to look for foods that have calories/10 grams of protein (or more). This equates to 40% of calories from protein.