This is a good topic, and a difficult one because it gets to a lot of questions about varying player tastes. No definitive answer–and we want people to keep talking about it–but a few thoughts:
One goal you have might be maximizing your chances at killing the boss. Another goal you have might be maximizing your position on a ranking website. Those goals sometimes lead you toward different behavior. It’s not really up to us to tell people which one to pursue. But we do design towards keeping the first one interesting and rewarding. Choices where players are explicitly thinking about maximizing the group’s output (things like external buffs, or group-level cooldown coordination) contribute to that. These can sometimes make the second goal less clear (for example, because buffs make it hard to account for everyone’s damage contribution), and so far we are okay with that.
Another way of looking at this is: the “killing the boss” goal is made by us. The “ranking” goal is made and managed by players. Players can–and should!–do what they want with it. Adaptations like asterisking logs which include Power Infusion are already occurring. The rankings are an expression of what players choose to value, to use as a mark of individual achievement. We all know that someone’s value to a group is not solely determined by their DPS meter, even though it’s a useful tool. Guild recruiters evaluating players know that various kinds of contributions aren’t reflected there. Contributions like Power Infusion aren’t obvious on them either, but similarly, that is an analysis problem left to players.
One of the most difficult aspects of this topic is social tension. Sometimes people argue with their teammates about buffs. It’s very understandable, to me, why one possible response someone might have for that is–this can put you at odds with your own groupmates, so stamp it out. The flip side of that is: this is part and parcel of playing with real people in a large cooperative group. And preserving the human element of group play in WoW, not boiling it down to predictable mechanical interactions, is an important value. See for example, the common lament that group-finder content has lost a lot of the human interaction from the experience. Mechanics that involve interacting with groupmates bring out both the good and the bad of that, and that might be better than having neither.
Trying to be as transparent as possible: so far we have not constrained our designs to require meter/ranking clarity and fairness, where doing so would compromise other values. On a gut level, a simple, compelling, familiar RPG concept is: a thing your class can do is give one person a buff. It’s a minority of abilities in WoW, but it would feel like a huge step to say: that is no longer valid concepting for WoW abilities at all–that enabling high-fidelity ranking is so important that a certain ability design space is closed off.