Yeah, that's why in my vision for FNC> RDM/MST I gave MST the possibility of some chain and gave RDM an ability that reduced STR and DEX by 15% while buffing MND and INT 20%. That way MST can still survive hits and RDM's magic attacks will be worth using. For your vision I could see dropping one of the abilities for a similar conversion of stats.
Edit: Actually honestly your RDM tank really does sound more like a MST to me overall. And with your various attacks and traits, have you considered theorycrafting your FNC to branch into DNC and MST? It'd be quite interesting to see what you could do with that.