The damage buff is incorrectly applying to enemies with full HP giving Rangers far higher 'sneak' damage than rogues can do.
You can reliably one hit kill anything with under 15 HP, and even if caught while sneaking, pick of enemies one by one each turn in the same manner, comparatively to which a rogues sneak damage wouldn't work once the enemies are no longer surprised, and the damage is a bit lower as well.
Once we have level 5+ available and Rangers get a second hit, they will be able to deal colossal slayer damage every round on their second hit anyway, but this would normally be limited to longbows as crossbows can only hit once per round.
Currently you can pick up a 1d10 heavy crossbow, and add the 1d8 from colossal slayer on top on every hit, giving a damage range of 2-18 against enemies on full HP.
You basically sneak around all the goblin areas and pick 90% of the goblins off one by one. Combined with a Wood Elf's mobility, even after you are caught you can basically continue retreating and one shotting most enemies each turn without them ever catching up to you.
It gets even worse in terms of being broken, because it is treated as a second attack effects that apply on every attack are added to it, I tested with a GWM greatsword using ranger, he was doing 2d6 + 3 + 10, and 1d8 + 10 damage on every hit because of Colossus Slayer. Meaning he had a minimum damage of 26.
