A feat is actually worth +2 to your prime stat, which is significantly more than +1 to two secondary stats. If you make a great-weapon fighter choose between +2 to Strength, or Great Weapon Master, then that's actually a tough choice. If the choice is between Great Weapon Master, and +1 to Con and +1 to Dexterity, then that's not really a choice; and it's certainly not a choice, four levels later, when both of those stats have even values.
The variant human is significantly more powerful than the default human, since it effectively has +3 to its primary stat and +1 to a secondary stat. That blows any other race out of the water. It's definitely not balanced against the default human, and you seem to be using the assumption that they are balanced as the basis for your mathematical model. Three feats give equivalent power to +6 in your prime stat, which is a lot more than having +1 to each stat.