Cmon, Tsubasa's importance was kinda proved by updates, but most part of community doesn't get it. She knows about Yasu's religion (Priestess of Fallen Snow IIRC), she understands importance of Akira, so she basically understands the rules of the divine game and definetly can interfere. If she would not be important, who would?
I had to go back and find that snapshot to perhaps reiterate what I meant.
I am not asking proofs of "Tsubasa being important"; I am asking "what do you mean by Tsubasa
being more important than we thought she was?" When it comes down to it,
his response brings nothing new to the table.
It could be mean that she will actually be a part of the fuckery. Or, as unexciting as it might sound, it could just mean that she's not just a piece of meat for tit fetish that does absolutely nothing to Sensei's relationship and mental state (which is already proven incorrect).
So once you ask yourself "what does he really mean", you'll soon get to a point where you either consider Selly deliberately foreshadowing something that is either plain obvious or something literally hasn't been implemented yet, or start assigning random and unverifiable importance to her because Selly has spoken so it must be true. For example, I've color coded your reply, and
blue means your further elaboration is needed and
red means a claim without sufficient evidence. And this is the part I meant "can only be proven by future updates", as I prefer waiting than conjecturing without knowing what direction I should go.