Mounts also take up space in your bags, bags which will of course be much smaller. Every bag space counts. With no guild banks, and much smaller storage space, your bank alts are going to be essential. You’ll need to remember to always post everything back to a bank alt, and to remember to get everything from the mail box to the Auction House. Which is only in Ironforge or Orgrimmar.
The primary goal of Conflict and Strife is to provide an interesting choice in PvP by allowing access to an extra PvP Talent. It’s not necessarily going to be a strong option for PvE. The acquisition of this Essence is via PvP, and is totally optional for PvE-focused players. While there may be interesting PvE uses for some of the choices, it is not expected to be a strong competitor on usual PvE criteria (like total throughput) on every spec.