As a sad before variation spec are viable and completely fine. Haste however in pvp is so so, you would get more out of crit. Haste effects cast time and DoT ticks, true that a faster cast time would save your life but we have take into account interrupts and such. Making instant casts more worth whiled and when it crits its just glorious, crit is just better for a pvp situation. Surge can crit, desperate prayer can crit, renew can crit, crit procs inspiration meaning a high up time, pom can crit (first charge = orgasmic). The only thing I don't think can crit is lightwell. Serendipity also makes haste less attractive for single target healing.
As for flash heal glyph you're right, for some reason I read below 10% health (lol). Since mana is an issue for holy taking dispel glyph would be lackluster over PoM since you know we cant stack regain and dispel spam like other healers... (GG blizzard).