I agree that RUN's defensive side needs to be bolstered more. The job needs more than magic evasion to be a successful tank. It just takes hits too hard and too often from anything difficult.

Using Paladin as an example since they've already started mirroring the job (example: PLD has the highest defense bonus and protect 5 but shell 4. RUN has the highest magic defense bonus has plenty of magic defense as well and physical defense capabilities. I would be completely fine if they just made Rune Fencer the evasive counterpart, magic and physical evasion.

I'd personally like to see Rune Fencer become the anti-caster job. So even if it's not tanking itself, just bringing it is enough

-Barlight & Bardark (no reason not to have them, not being in the same so far is not a counterpoint)
-Possibly other barstatus spells such as Charm, Stun, Dispel
-Possibly lowering recast of Ward: Liement
-Natural Evasion Bonus or if wanting something not carbon copied from other jobs, then Parry Bonus trait.
-Maybe meritable or natural spell interruption down.
-Reworking of Blink to scale number of shadows with enhancing magic.
-Increase the potency of avoiding an attack with foil given it's short duration. (I find I'm more likely to avoid a TP attack with Flash rather than Foil. Given that it only protects me versus how Flash protects anyone, it should be more accurate.)
-More gear with +parrying or +evasion combined with haste gear for TP. (a more evasive/parrying/resistance version of the PLD empyrean set would be nice.)
-Riposte: Attacking after a successful parry (could be a spell, job ability or trait)
-Reflect? (I know players have clamored in the past for RDM or PLD to have it (myself one of them), but it might fit in with the whole parrying/countering magic)
-Devouring Magic: Some ability to remove a buff from a monster and heal the Rune Fencer.
-Spell Amensia: The ability to temporarily silence a target for a few seconds, locking the ability to cast that spell for an amount of time.

Just pitching ideas. The adjustments listed are a good start but I agree there needs to be something more to make it a viable tank on more difficult events, especially with most of them casting multiple elements.