Interestingly, I got a conclusive answer to this question when working at S2 on Heroes of Newerth. The CEO accidentally CC'ed me (he meant to CC Sean, not Shaw

Interestingly, I got a conclusive answer to this question when working at S2 on Heroes of Newerth. The CEO accidentally CC'ed me (he meant to CC Sean, not Shawn) on a letter from Valve's lawyer threatening us with legal action for copying Beastmaster's mechanics. They had a side-by-side of ours (https://hon.fandom.com/wiki/Tundra https://hon.fandom.com/wiki/Tundra) vs theirs (https://dota2.fandom.com/wiki/Beastmaster https://dota2.fandom.com/wiki/Beastmaster), and pointed out that the mechanics were identical. It was very surprising. So the answer is "Maybe not, but that won't stop companies from threatening to sue you." Or "Maybe it is, and companies will threaten to sue you." No one really knows, since it hasn't been tested in court.