That's exactly why, though. Farming TX efficiently means dropping Witching Hour for Goldwrap, two dps gems for Hoarder and Wreath, cubed CoE for Avarice, and at least one dps passive for Hot Pursuit. That's signficant dps lost to movement speed, so you need to keep everything else you possibly can if you want to still 1-2 shot everything.
Cold also applies bonus dmg from Cull the Weak (which replaces Ballistics) on the first shot, whereas fire requires Thrill of the Hunt to apply it at all, and even then only on the second+ hit. It's much harder to gear for, mainly due to having to find a perfect cold SoJ, but the build does more damage than the fire version with even faster movement. [For TX farming only, fire is still better for GRs as Pyros said.]