Agree on the invisibility, and that's a poor running of invisibility by most GMs - it absolutely does not mean automatically hidden in the same way that a creature in total darkness is not automatically hidden, nor should it be construed that way - the Invisible condition clearly states:

An invisible creature is impossible to see without the aid of magic or a special sense. For the purpose of hiding, the creature is heavily obscured. The creature’s location can be detected by any noise it makes or any tracks it leaves.

It is incredibly frustrating to have inexperienced GMs run invisible creatures as being able to take potshots at the PCs with zero fear of retribution except by wild swings at empty space, hoping to get lucky. Aside from the advantage/disadvantage on attack rolls, all being invisible does is allow a creature to hide without needing any kind of cover because they're already heavily obscured, and prevents creatures from perceiving them with normal vision. A perception check against the hidden creature's stealth roll, truesight, blindsense/sight, tremorsense, and the creature making any sort of noise (such as with an attack) immediately reveals the invisible creature's location.