
My experience:
Currently, the Marrowbreach seems to be about the same threat level as the Nibbler-Mango. During my first encounter with it at one of the colonist habitats, I loved when my PDA said I was being hunted, and I was careful to avoid the Marrowbreach. It felt like a cat-and-mouse chase, it was great. But when I inevidably got hit, all that went down the drain. The thing did something like 5 damage when I thought it was a real threat. I have been playing for close to 10 hours and ever since that (which was in the first hour of gameplay), the Marrowbreach has been completely ignored. When I see the creature I don’t even bat an eye. It turned from a mid-level threat to something that demanded no respect or attention.
Problem:
I think the implementation of the Nibbler-Mango is great. It is annoying but not a threat to your life, and I think that is the exact problem. The Marrowbreach is no longer a threat, it is just annoying. It doesn’t do enough damage, (about 5 in my experience). You can sit around and ignore it for 5-10 minutes, and even then there is no guartantee you will be threatened, as the passive healing helps you recover most of the damage it does.
Potential fix:
I think the Marrowbreach should have increased damage, for example, it could do 1/4 or 1/3 of the players health. Not something as dangerous as a leviathan, as the Marrowbreach is too plentiful for that, but something that demands respect and attention. Especially considering the many ways to deter it, including flares, the dash ability to run and hide, and the Sonic Resonator to stun it, I don’t think it would be too much of a nuicance if it did more damage, but it would add a new level of immersion and danger especially in early-game. It might make you think twice before you go right through its path with just your wavemakers and survival tool.
The only problem with this is sometimes they get bugged and won’t leave you alone for anything.

Agree, additionally I think the bigger Marrowbreach in the fire Area should do more damage than the juvinille. Lets say 25 for juvi and 35 for adult.