Only time I charge up meditation stacks is pre pull, during invuln period and when invig is on cool down and i don't have enough tp to use my next ability. One meditation stack is enough to delay my gcd enough to restore the tp needed for my next ability and I continue this until I reach 5. This way you're less likely to lose GL3. Realistically the only time I use purification is on A2S. Every other encounter has enough downtime where you won't need it if you have BRD/MCH/NIN in the party.

As far as dps goes, don't fall into the lazy rotation of using the 3 flank moves, 3 rear moves, 3 flank, 3 rear, repeat.