Well, pick one.
An interesting and engaging story...with all the negatives to characters that come with it.
or
A boring and uninteresting story...with all the invulnerable and indifferent characters that come with it.
You don't get both. If you want an interesting and engaging story...you don't get to have invulnerable and indifferent characters. One literally precludes the other.
I think what you'll find is if you indulge the interesting and engaging story, the players won't want invulnerable characters. Because you have set up a power struggle at the table where you feel you need to "curb player power", players will automatically pull against you.
The basic question is, who is unhappy here? If the players are perfectly happy but you aren't, they aren't the problem. Neither are you. The problem is, you are the wrong DM for that table. It's a very difficult thing to ever admit and even probably harder to do anything about, but, there it is. If you are the only one at the table who has a problem with this, then that's on you. Instead of trying to have the game force these players to play the way you want to play, you need to find a new group who agrees with you.
Because the other route- having rules that force preferences just leads to toxic tables and more problems. Because no matter what changes you make, the players are going to automatically resist them because it is so one sided. "Your character is too powerful for the game, and I know better than the game makers, and I know better than you, so, we need to change your character" is NEVER going to go over well, no matter how well you phrase it.
One suggestion I will make though
@overgeeked that has helped me with this sort of thing. TRACK the numbers. Don't go with your gut because your gut is wrong. It is always wrong. Stupid gut.

Keep a record of damage done per PC, success rates per PC, whatever. Do it for a couple of sessions.
THEN start talking about the need for changes. Because if you're just basing this on your own observations and no actual empirical evidence, I can guarantee that your observations are wrong. Personal bias is too strong for your observations not to be skewed by it. Every DM in the world is guilty of this - myself just as much as any other - and you need that empirical evidence before you can make any sort of definitive statement.