Bits are only painful in the wrong hands/improper use. Stating so, I feel, is a bit uneducated.
The softest, mildest bit a horse can use is a loose ring snaffle. If not a loose ring, then a french link.
Hackamores can be just as dangerous/painful for a horse as (if I remember right) it relies on facial and poll pressure. There are a lot of nerves in a horses face.
If you are yanking, pulling and being heavy handed on the bit, of course a horse is going to fuss.
A well trained horse can be ridden in the mildest bits. Not "deal" with it. It gives clearer instruction, and some actually quite prefer bits verses hacks or bosals. Some are indifferent. Some can't handle bits because of how their face is structured.
I think maybe you should do more research on bits and bitless riding.
Metal bits in the mouth = Less Horsemanship, more pain, and a lack of partnership between horse and rider.
Any horse can be saved from the bit if they are prepared and set up for success. The result= a happier horse. Any well known professional trainer will say that the most supple horses they have come across are hackamore horses. This is because the horse is not being forced to act as asked, but rather does because he was taught. I can say the word "left" and my horse knows to turn left. I say "right" and he turns right. I can say "whoa" and he knows to stop. Right now, he knows 25 verbal commands. 80% of the time I don't have to touch the reins to his neck. My gelding is 5, he's got a lot of learning to do, but I set him up for success with confidence in him 100% of the time. I'm not his master, we have a partnership. We have to, I am putting my life at his discretion every time I climb on his back. I'm not going to put a bit in his mouth and force him to do as I say, I just don't see the point. I'm not afraid of him, and I certainly don't want him to fear me. I want respect, and I show him respect in return. A loose ring snaffle and a French link snaffle most certainly are not the kindest bits. Technically the kindest bit is a Myler combination. It's designed to apply nose pressure first, then mouth. And the joint is completely enclosed so it cannot be bent in half. Snaffles pinch the tongue no matter how you pull it. Try putting the snaffle on the soft part of your arm, or better yet on your tongue, let someone else pull back as if trying to stop a horse, or pull for a turn. It hurts. When a horse is in training, he doesn't have a bit in his mouth he has a halter on. The halter applies nose and poll pressure. So, the horse is always confused and upset when that first bit is put in his mouth, he has no idea what is going on but he still tries to choose the right answer. When the horse doesn't give to the first light tug, the trainer tugs harder, and harder until he does what is being asked. The horse learns what to do. Why not keep that same halter concept, and stay off the bit? This makes more sense to me. Snaffle bits shut off the horses air passage, drive into their tongue, pinch them, tension in the mouth puts tension throughout their whole body.
Here is a great description of how a snaffle works for a horse. Fast forward to 3:40, where Dale Myler demonstrates the snaffle concept on a girls arm. This is the most informative information you could ever receive about snaffle bits. And if you use them, I DEFINITELY recommend you to watch the whole thing. https://www.youtube.com/watch?v=MqGXCWVSS0Y
Here's a link to a video of how the bit effects the horse in light or heavy hands: