I disagree.
I think they are HELPING WWE financially.
Certain studies show that, when two similar products are not in direct competition with one another, their dual presence in a market can be mutually beneficial. Both WWE and TNA seek to maintain AND attract new audiences. It is feasible that the first professional wrestling experience for a young, new fan is TNA, and their product makes that same fan want to check out WWE.
Since TNA doesn't directly compete with WWE for ratings, it is VERY possible, even likely, that TNA's presence creates additional interest and increased revenue for WWE.