Thank you for bringing this up.

While every job have their instant cast stun, silence, heavy, knock back, etc., BLM's tool kit needs to be cast, set up, and triggered! Hence, here are my opinion to make it at par to the rest of the jobs.

1. Change Burst to instant cast.
2. Make Half-sleep do something! Maybe apply heavy or slow! While waiting for the sleep to take effect, the target is either gone far away or killed you! So why not....
3. (OPTIONAL) change Astral Fire to Burn, with increasing debuff time with every fire spell maximum of 12 or 15 seconds. When triggered by Megaflare, it will apply the combined Dot potency based on the remaining time and removes the debuff.