Entei is so selfless it will willingly weaken its own attacks for the sake of its brothers!
...anybody?
Anyway, so do the Legendary Birds. Considering two of them get Hurricane to abuse it, it makes a tad more sense for Moltres. Other Fire-types to learn Rain Dance include Heatmor, Litleo and Pyroar, and the Fennekin line. None of these get Thunder, Hurricane, or any Water move.
Meanwhile, there are Water-types who get Sunny Day! These are: Slowpoke and its evos, Vaporeon (Eevee), Corsola (have fun with that 4x effective Solar Beam), Remoraid and Octillery, Suicune, the Lotad line, Surskit (Bug-type, so I guess it helps), Bibarel (but of course), and Palkia (what 4x resist?). And Volcanion, but that's trading one STAB for another, much in the vein of Moltres in the rain.