Not really. The main reason Warrior is essential is because of the Storm's Path/Storm's Eye debuffs. These allow Warrior + Dark Knight and Warrior + Paladin to be more optimal with any combination of healer and dps than Dark Knight + Paladin.
A 4th tank might make the current situation worse or end up leaving the current situation mostly unchanged. Warrior + Dark Knight/Paladin/New Tank being optimal is not a situation I want to see and Warrior/New Tank + Dark Knight/Paladin is hardly better than the current situation.
The healer problem is more because of how underpowered Noct stance shields are for PvE content in comparison to Scholar shields. White Mage + Astro(Noct) is just not as good as White Mage + Scholar or Astro(Diurnal) + Scholar even though it is still viable.
I'd rather see Samurai be a Katana wielding Maiming gear wearing slashing DpS with its main combo applying a version of Storm's Eye/Dancing Edge with one of its secondary combos applying a version of Storm's Path. This should solve the "Must have a Warrior" problem.On Topic: I personally would like to see SAM Tank and RDM DPS using a Sword or Rapier of the likes, would satisfy both sides. Just my opinion though.
I'd like Red Mage to be a Rapier and Buckler wielding Scouting gear wearing melee piercing/magic support DpS.