So I saw the Aberrant Mark feat and saw that only sorcerer spells can be chosen. So I looked at other spell lists to see why this was the case. So the only thing I could think of was a dwarf fighter with this feat. Dwarfs get a +2 to CON and don’t need strength for heavy armor. With the feat a Sword and Board build would become tanky since it can use heavy armor and cast Shillelagh to use CON for damage, and Hill Dwarfs get even more HP. Is there any other things you can do to with this feat that I missed? And how can we modify the feat so it doesn’t allow this?
So as some others have stated, it's mostly an Eberron lore issue. Not only is the sorcerer spell list the one that includes the most destructive type spells, but aberrant marks are typically tied to bloodlines and mutations, similar to true dragonmarks. Thus, the power of any dragonmark, aberrant or true, comes from within that individual. This is exactly the way the origin of a sorcerer's powers are described in the PHB.
However, I think it is best to use this as a guide, rather than a hardline rule. Others have mentioned spells, such as speak with animals and inflict wounds, which would be appropriate.
If you want a good story to mine ideas for aberrant marks, a great example is in the Eberron novel Son of Khyber. This story shows a number of ways aberrant marks might manifest. For example, there was a dwarf with an aberrant mark that allowed him to regenerate from any wounds he took, but each time he regenerated it was from a different creature. He had an arm like an ogre, patches of skin resembling that of a kobold and troll, and an eye like a snake. However, his powers were also a curse. For example, he couldsurvive a sword through his heart and keep fighting. But the heart might regenerate into a halfling's heart and be too small to pump the volume of blood he needs, incapacitating him. His friends would have to cut into him and remove such organs until he grew one that was compatible with his body and sufficient to sustain him.
That is an important thing to remember about aberrant marks. They do grant their bearer power, sometimes great power. But that power always comes with a terrible curse, usually in the form of some corruption of the mind, body, or soul.