Invisibility and Chameleon need to stay IMO, however, they should be more costly and time consuming to cast.
The real issue isn't in the spell, it should only be used by really high level Illusionists anyways, the problem is in AI reaction to the spell. It should be readily apparent to many AI when there is an invisible predator lurking around, unless they do absolutely nothing to give themselves away, after all the spell only effects vision not scent, hearing, or even seeing the consequences the person has on the surrounding environment. Fact is the AI should look for help, call out that there's a mage in the area, swing in the direction of sounds and search out for enemies, entering a higher alert status when something is amiss.
To further this, higher level enemies should have tricks up their sleeves for just such an occasion such as smoke which could reveal your location through relatively limited processes such as particle effect physics, or traps designed specifically to reveal such individuals. Floors that are notably difficult to be quiet on, or chains hanging around, and vines and such that would give away an invisible player, even shallow water would have this effect. Top it off with our magical opponents who could simply cast a spell to undo the invisibility or chameleon, or even better silence you altogether.
Plus following the tradition of RPGs there are vocal and somatic components to be considered with all spells, and these are no exception.
Point is this can be solved in game without just taking away the effects, and don't even pretend the technology isn't good enough, it easily is, even for consoles.