The link I provided shows you how Robes have poor Physical defense, practically like people have stated... add more Vitality points to increase your Hit Points for higher leveling:
Feeder = level 71
Samurai = 73
Paladin = 75
... However, you can wear better defense armor, Leather, Scale, Chain or Plate for the physical side, well Scale has better universal defense.
Monk = 77
Ninja = 79
Warlock = 81
... They can only wear Robes, so you are at a disadvantage in defense. More Hit Points or more Enhanced Effect... up to you and your play style. Not really great for tanking in a full group, but that depends on the casters in group for healing.
Headhunter = 83 (woot Scale)
Alchemist = 85 (back to Robes and no weapon choice)
Monsters level up as you level up, and to be honest, level 75+ and monster damage increases quite a bit, and then Robes have less physical defense.
Personal choice... more Vitality or Enhanced Effect... once you become accustomed to the damage, you can equip your build appropriately ... I like + Stat items, no Enhanced Effect, however the Abilities I use are based on being Hit / damaged to charge them up, not on me attacking. My Play Style... also I always Heal, even if I am a Barbarian, Samurai or Paladin etc.
You will come to your own conclusion.
Oh, I only use a 100 vitality base cap and 30 intelligence base cap. Salvation / Retribution on most builds and Stat Armor and Main Charm... 120%+ EE Heal type charm in ACC slot.