When a rune description doesn't say "also", does that mean that the main skill ability is overwritten by the rune (the rune essentially replaces the main ability)? Or are all runes meant to be in addition to the main skill effect, whether or not the word "also" is used?
Just want to clarify, pardon my ignorance. Thanks in advance!
I'm not sure I'd expect Blizzard to be 100% consistent with their use of "also" versus "in addition to" or any other such terms, so I'm not sure I'd want to give an answer based on the language alone. In most cases a rune effect is fairly intuitive and adds some feature to or increases the values of the original skill. If a rune effect is totally different from the base spell, there's a good chance its effects replace those of the base spell. The "Arcane Orbit" rune for the Wizard skill Arcane Orb replaces the effect of the base skill, for example.
I've always assumed all runes add to or increase the base skill unless it explicitly says otherwise or the new effect is obviously incompatible with the base effect. I don't really trust the tooltips, though, so ultimately we're going to need to test them in game to know for sure.
In most cases its clear what happens as it says increases/replaces etc. The only iffywashy one is to my knowledge Hammer of The Ancients Rolling Thunder, cant tell if it removes the base skill hammer damage or not.