Can we make shatter grant less personal armour and the aura scale with bonus magic resist instead of flat armour? Obviously up the ratio on the aura since it's bonus only.
This would stop the double/triple dipping and give taric a good (and supportive) reason to buy and rune magic resist.
You could also split the passive damage ~60/40 between armour and mr.
From there maybe up the shatter damage ratio slightly to compensate for the list armour.
Also. Why not make his ultimate damage and ap scale from mr too? Seems like a good place for some support scaling that would, again, promote less armour stacking.
I want him less powerful in terms of his multiplicative scaling. But I really want him to stay tanky and supportive. Heck, I even want him to have his top lane options.