Yeah well. It's a Herald.
Edit: briefly forgot it was a solo Herald.
Here are some things that you can do to improve damage output:
Lose the large shield. Or better: make a weapon setup with a small shield. -8 accuracy is a bad drawback for damage output. I'm sure with your regeneration capabilities you can do with a small shield, too in many situaltions. If you want to stay astanjy as possible all the time you will have to accept that your damage output is less important than your survivability and that you simply have to outlast your enemy.
You can use Brand Enemy, put it on every enemy (auto hit, fast cast, no recovery). The damage bonus of Sworn Enemy also works with everything. It's Zeal well spend imo since the DoT will last until the fight is over. It obviously doesn't work on fire-immune enemies. It even heals fire Naga and Dorudugan. So in that cases don't use it. Besides those situations it's a great smash tool for somebody who needs to outlast enemies (and has low DEX).
Increase DEX with items and consumables. DEX is the most impactful dps attribute in the long run.
Use Eternal Devotion every once in a while. The +15% lash applies to almost everything (except damage over time ticks), including invocations such as Her Revenge but also Sacred Immolation.
With more DEX and high INT even Inspired Beacon's +40% dmg can be useful. But I personally would spend the Zeal on External Devotion and Brand Enemy. It's a waste of Zeal if you are solo imo.
Use Sacred Immolation. With Sacred Immolation usually a Herald's damage output will go through the roof compared to before. With your high RES and some "-x secs/-y% hostile effect duration" items which are great if you are solo you can make it so that the annoying self damage part runs out a whole lot sooner than the fire aura itself.
Prepare a chant with Come Soft Winds + Dragon Thrashed. As soon as you feel that healing isn't needed as much: switch to that chant without(!) Brisk Recitation. Check if the enemies suffer from both DoT effects after both phrases have passed. If the enemy have both, switch on Brisk Recitation. You will have a lot faster phrase generation, but the hostile effects on the enemies will get refreshed enough every 6 secs that it won't run out. You will deal chant damage as if Brisk Recitation was still off, but you'll have the benefit of faster phrase generation. Come Soft Winds Wil heal you a bit, too.
You can add Blackened Plate (Death in Life) for a little more raw DoT. But I suspect you might be inclined to use the healing enchantment instead.
If you want to add even more DoT damage to your chants and other actions: pick up the Great Sword Effort and enchant it with "Hemorrhaging". You don't need to skill anything for the great sword, it's just a tool for chanting/casting. Pick up Hylea's Talons (Gloves). The Hemorrhaging attack (hobble/sicken on crot) gets triggered by offensive chants and invocations as well (if they crit). The hobble/sicken attack of Hemorrhaging counts as a weapon attack so it will trigger Hylea's Talons potent DoT on enemies (but on you, too unfortunately). Make sure to out heal the gloves' damage.
If you combine Dragon Thrashed, Come Soft Winds, Blackened Plate and Effort+Gloves you can already melt foes without actually doing anything. Add Brand Enemy, Her Revenge + Eternal Devotion and later Sacred Immolation and you should be a terrifying damage dealer without even striking much, so the low DEX doesn't matter much.
The good thing is: you can switch from healing/tanking mode (weapon + shield + healing chants) into damage dealing mode (Effort + Gloves + damaging chants, Sacred Immolation etc.) in an instant. And switch back if needed.
This adds a lot of versatility. And versatility is always good. For example if you can place yourself into a corner or choke point you might be able to switch to the offensive mode. Or if you have Animated Weapons out which should be able to tank for you for a little while.