It was improved, then they removed Shield of Righteousness and it went back down to crap. They reduced Exorcism's cooldown making things a little better but they reduced Inquisition's duration making it a DPS loss to try to keep the buff up. Holy's DPS has been a series of "one step forward, one step back".
Oh and then they doubled mob hp values to make matters even worse.
I doubt leveling as holy will be anywhere near as fast as the other two specs. As far as I know discipline and maybe holy for priests are the only healing specs that can be competitive at leveling. Buttttttt I don't have beta so I may be completely wrong.