This is simply ludicrous. Be that as it may, having no need to take the high ground (if you don't need the extra advantage) is still an advantage. Being able to make other kinds of attacks besides ranged attacks from height with advantage is still an advantage. Negating the disadvantage from shooting up is still an advantage. Even if you built your entire character as an archer who maximizes advantage from height, even your entire party, Foresight would still be an awesome spell to have in your arsenal.
It's pretty easy to see which one is still better, and the fact that they are not mutually exclusive only makes both abilities even more powerful. With Foresight you can shoot from a tree into a cloud with no disadvantage. You can shoot your bow at an enemy in your face with no disadvantage. Without Foresight, disadvantage. Even at level 4 I am seeing enemies with 3-4 conditions stacking to determine advantage. Imagine at level 18 or whenever Foresight becomes available.
The main issue is that high ground shouldn't be as potent as it it.
High ground literally trivializes this fight and it shouldn't. (also bonus action hide). Should these homebrew mechanics be this potent in every encounter?
No, they absolutely should not be. With how frequent verticality is in the game, high ground currently is a lower cost foresight. You don't even need another character to use it, you just spend movement or move before combat starts.
Should characters be getting free foresight because of where they start in combat? (Simply no, it makes no sense).