New BLM, rotations questions and advice

[Allyrion]

Ppl wh suggest using flare glitch under umbral 3 clearly does not parse dps. Those flares for me hits for 450 while normal astral 3 flares hits for 1200.

It hits for 450. What does your fire III hit for?
Even if it's more, Flare hits multiple targets for that damage and this is about AoE usage. It doesn't drain your mana under Umbral Ice so you'll get another Flare doing the Astral damage right after.
So yea, your flare hits 3 targets for 1350 and then you get a 1200 x 3 flare right after. It only replaces Fire III to convert your stacks but has higher base potency and an aoe effect.

If you choose to use a glitch is up to your own discretion, but the dps is better.