I believe the issue lies with the role DRK is given being a Tank.
Being a Tank the focus will be more on defense rather than offense. Usually the massive explosion stuff circles around a job that does DPS because it heavily emphasis on it showing heavy damage visually. As a Tank the visuals will be better fit into using Darkness to shroud the DRK for protection which can still be visually effective if they put visuals more into how Darkness protects through shrouding the Tank so it will not be visually explosive on attacks that does massive damage but more on the lighter animation for attacks to emphasis that they are more done to attract the attention of enemies rather than dealing massive damage on enemies. They still kill but not to a point the animations is explosive.
As for Red Mage, well I think it is more of the identity crisis of Red Mage being either Range or Melee compared to a Spellsword and Mystic Knight which are heavily focused on being melee Magic attackers or tanks compared to Red Mage that always struggle being both a Melee and Range Magic attacker in FF games. Not to mention most incarnations of Red Mage in FF series is that Range Magic is the main focus of attacking and double casting it while the melee aspect is secondary or never used.
You got both Range and Melee attacks but the job can only focus on one path as the main attack focus. If they go melee the player base will still just use all the range attacks for melee range because they will just build the energy to cast the Range magic then unload it in melee range. Then if they go Range as basic attack focus and Melee second we have what we have now being Range Attack then only go melee if we need to unload the 3 hit melee attacks.
By job identity design, a Spellsword and Mystic Knight will be better suited to be a Melee Range DPS Job anyways since they have a more linked identity to be more focused on Melee Magic attacks compared to Red Mage which most incarnations focus on just using Range Magic attackers and double casting them.