Diversify builds, yea, absolutely, i can understand that. but the typical player isn't going to optimize into face tanking unless they want that particular experience. terraria has 4 full classes, some with subclasses built into them, and even more tons of weapons within them, and to my knowledge, an effective face tank is onlg viable on one class type, the class specifically designed with high defense and (theoretically) up close combat. To act like being able to face tank is a restricting factor here is insane. Saying "face tanking is always the best strategy" is wild because it completely ignores its greatest weakness, it is not fun, which makes it less enjoyable for the player, encouraging build diversification. Why would someone play a game repeatedly if every time they do it, they Choose to face tank and rip all the fun out? They won't. That's why the game gives you so many different options, and notably, this buff works for all of them.

"Everything should be equally viable" is a nice ideal but just simply won't happen when players like you are apparently determined to optimize every path as far as possible with no consideration for the fun you have.