I don't mind the game having vision cones, but they should differentiate between hearing and seeing. This way you can't sneak up with someone in full metal plate without a good skillcheck just because you managed to avoid their vision cone.

For example:

- In vision cone = stealth vs. passive perception check
- Outside of vision cone = stealth vs. penalized passive perception check (maybe with -5 like RAW for disadvantage conditions, depending on the character, but that might be too much)

Visually, it can be somewhat like the Pillars of Eternity stealth cones (but larger):

[Linked Image from i.imgur.com]