If you bring that to a level where people will say "If we have a PLD tank, we definitely don't need 2 WHMs in our party", then I'll believe we can achieve a balance.
I like this thinking too. Perhaps let Divine Veil work with Holy Succor or just give Paladin another cure ability to eliminate the need for a second White Mage. If Warrior can bring DD and tanking to the party, Paladin can bring healing and tanking to the party.