Guan Yu, the undying

You already have pretty good teamfight heal in Conviction, and you're doing what you can to enhance it with Caduceus Shield. If you build too much into a reliance on healing and sustain, it just makes anti-heal affect you that much more, rendering multiple items less effective.

I can understand the appeal of high health, and between your choices of Shield of Regrowth and Blackthorn Hammer, you've got plenty of that. What you're lacking (quite a bit of in fact) is protection. You've included Pridwen, and late game you also have Spirit Robe, but that's not really making you as tanky as you probably should be. Keep in mind, both the shield and the following damage from it are based on the protections you have.

If anything, you should consider replacing Stone of Gaia with an item providing protections...you can consider Gauntlet of Thebes for a huge boost of overall protections, or you can target the higher damage threat (physical or magical) with other specific items like Oni Hunter's Garb, Midgardian Mail, etc.

One other thought...at late-game, you've got 50% CDR. Depending on what you've chosen in the rest of your build, you might consider dropping Blackthorn Hammer.

In actuality, you might also consider a revamp of your build order too, and possibly even replace Blackthorn, Pridwen, etc. Breastplate of Valor is often picked up (and is a good earlier CDR alternative to Prid if you get it early-game), and you might consider delaying Shield of Regrowth a bit later as well, so you can build more protections earlier.