I have noticed this myself.

As SCH - Adlo/Succor/Sacred Soil take time to properly come into effect even when shown.

As BLM - Firestarter procs. As you said have to wait for Fire to reach it.

Although you can claw a little back with BLM by: Having Umbral Ice III up, you can Fire III to get Astral Fire III and you can still cast Fire I quickly as if you had Umbral Ice III, even though you've switched to fire and you'll still do the increased Fire I damage. (And at the reduced mana cost!)