Taric skins do suck, I like the functionality of the champ, but it is lacking so much. He has no mobility and his stun often wears off faster than it takes to land, so by the time you see it hit the enemy has killed your adc and run to the turret.
I see why the stun is slow to land, but it is so short, it should last a bit longer (0.5 seconds?) I have often thought that his ultimate should be a knock up, then though, it would be overpowered, he'd be like bard, a super strong and effective ultimate, with no other skills to help him out inbetween. His real weakness is that he can't chase or effectively peel, when I play as him, I often just beat on the enemy adc trying to kill mine, and watch as they are shocked by how much damage this "support" is dealing, but once they kill the adc, they escape, even with flash and stun, he can't chase, and his stun is so weak he cant stop them. Because he is melee, he needs to get close, so your adc usually runs away, out of your heal range and even out of aura sometimes.
His ultimate plus w means with a graves or jynx, its instant kill, and the low CD make it effective, but I think he needs to close distance. A speed buff or mini dash might do it, but otherwise he just needs a longer stun.
His heal seems fine, buffing it seems too much (speed buff on his heal would break that one skill)
His W is already complicated enough, knowing when and how to use it can destroy enemies or youself
his passive works as is and shouldn't be modified either
this leaves his ulimate and his stun. If his ultimate is made stronger, it doesn't help his kit, just makes him a kind of nuke that needs allies to be effective (trust me + 70 ad and ap late game is strong enough) adding a knock up would be great visually and make it more useful, but it doesn't need it, he needs something more reliable than an ultimate, leaving his stun
there's no sense in his stun having a speed or dash mechanic, so all that's left is a passive ability or longer duration. (it would be nice if he smashed the ground and a fissure travelled to the enemy target resulting in a knock up, same mechanics except more time to reach target and synergy with other champs - plus it would look cooler than a sparkle to the face, and make more sense considering his weapon)
Besides longer duration, a passive that cause slow to nearby enemies (did he have a similar skill in the past but got nerf'd, or am I thinking of another support tank... oh there is a similar one in Dota2 lol) anyway, if his q passively slowed enemies near him, improving his peel and chase (once he gets close), OR if it had a slow mechanic that laster after the stun (not as great synergy with his kit, but better) I think his other skills would supplement him towards a higher pick rate
some kind of slow mechanic on his Q, and/or a knock up instead of a stun (with higher stun duration) that simple change would make taric effective in my opinion