I personally think sneak should be disabled in combat completely, although I've been abusing it in my own solo runs.
First reason, is the combination of sneak and rain/contamination, the player gets to sneak while the enemies treat the player as if he is invisible and unable to locate the player, and die in poison zone eventually, I was able to beat the Dallis encounter at level 3 using this method and I didn't like the fact that I could do it.
Both of those skills break Sneaking and have a short range, so clearly you're talking about NPC's and not enemies. The fix you want should be to the AI and coding of surface ownership. Although that might have been the case at one time and changed back because it unintentionally produced a lot of unwanted NPC hostility.
Additionally, it seems like exploiting that method to kill NPC's is a tedious, slow, boring way to play. That's punishment enough, and so I do not think it needs to be changed.
Second reason, is that you can freely stall for cooldowns in sneak, you can kill an enemy on high ground, out of enemies' sight range, sneak, wait for all cds to be back up, go in again. I think, having only chameleon cloak as invis and stall method is a sweet spot, anything more is simply overkill.
This is another tedious method, so again, I don't care and I don't think it needs to be changed. If someone wants to sabotage their own experience by doing this, they should feel free to go ahead.
Thank you for the example. Nerfing that is exactly, EXACTLY the kind of punishment which would hurt a lot of normal players just to stop a few compulsive cheesers. I am therefore not a fan of that approach.
No one is forcing you to cheese the game using Rain + Contaminate to kill peaceful NPC's, no one is forcing you to use Sneak to wait for cooldowns to expire. If you do not want to use those, then do not use them.
As for guerrilla, can really just treat it like rest of the 10 bad talents that were never properly balanced, and assassinate as a combat opener,
I kinda think that the 10 bad Talents should be properly balanced.
I'm not a big fan of Skills which are only useful as combat openers and are bad after the fight begins, which is why I consider Assassinate in its current state as bad and in need of change.
or make it so assassinate deals bonus damage when out of sight range of enemies, regardless of whether sneaking or not, and tune the bonus damage numbers as well the cd of the skill.
Hmmm... can you define what you mean by "out of sight range" of enemies? Do you just mean "outside the range of the vision cones for sneaking, or, as I suspect, do you mean "from the next county over, so far away that the enemy can't actually reach you without spending 8+ AP to move"?
Because if it is the latter, see my previous response about disliking skills which are not practical to use after combat starts.