Each of his abilities typically has 1, maybe 2 uses. His ult is the only loaded part of his kit. His Q is a pretty standard, low range stun thats dependent on a variable and the damage on it is SHIT. barely crawling over 200 at rank 5.
His heals are pretty on par with other healers in the bottom lane, except he has to wait more time and can never 'clutch' heal. Sure he can set them up at the tower which is nice, but he will never be able to completely revert aggressive burst the way shields or straight heals do.
His magical journey has about one use, hardly overloaded, long cool down, even enemies can follow, supportive initiation tool.
His ult has many uses, its clearly the focus of the designers when they made him. But it will take skill to use properly, You use it on an enemy team at the wrong time and you may waste cool downs of your allies, use it on an improperly positioned ally and guarantee their death.
His passive, it scales up in damage the more you collect chimes, which I suspect are the frequency of Thresh souls in number, except they're not spawned in a max radius around you. They spawn ALL over the map, so a certain percentage of them you are unlikely to get. Even still, the damage only increases by 20 every 3 stages or so, thats a lot of collecting them and him taking risks to get them. For 20 or so damage. The slow attached to it increases as well, to a max of 80% for 1 second. A pretty standard cc for a support type in late game.
I cant accept that you think he has an overloaded kit, when many of his abilities typically have 1 or two functions.