This is just the tip of the iceberg. Unfortunately I don’t think it can be fixed in the current implementation of the game. Maybe with a Conan Exiles II using the Unreal 5 engine.
For starters you are right, players need to have the ability to be more active in fights against bosses, granted you can now if you understand the mechanics, but spending 20 minutes rolling around and swiping at legs isn’t very heroic.
Second the Thrall system, while allowing for faster boss fights, isn’t very heroic either.
This whole player as a hero goes much deeper though than fighting bosses and not being able to dent high level player thralls.
For starters look at the gathering system. While typical of survival type games (and any changes to it will be met with a large clamor of "but it’s a survival game, that’s the way it’s suppose to be) it certainly isn’t heroic for players to do all the heavy lifting while thralls stand dull eyed around the base. Not much of a hero if you spend 2/3rds of your time in game farming stone, iron, and wood.
Honestly Conan should break the survival model, not pander to it. Thralls should be squishy, they should die, they should also be instrumental in both raiding, defending, and farming. Most mid and endgame systems should revolve around the thrall system in more indepth way than tanking and damage output. They shouldn’t be any better than the player, their stats level as the players does (allow them to go to level 60, but let them level up without following the player). Allow the player to bring more than one with them (with leadership feats that costs trait points increasing the amount players can bring and allowing for simple formations and more in depth commands.
Early game should be typical survival. Find food, shelter, and water while avoiding things that are stronger than you.
Mid game should open up after you get your first thrall. Here is where you stop worrying about your own survival and start to focus on maintaining a base and cultivating a following. Thralls can be given orders to gather. Have them go off into the world to fill their inventory with what you tell them to get. Have them be actual entities in the world that can be attacked by other players, or world AI. If you tell them to get the basic resources that are everywhere they will probably be fine, but if you tell them to gather say brimstone or demon blood, or something that requires a long trip for where you have set up they might not make it back. You could either go with them to escort them, or assign others to them as guards to increase their chances. The thing is they will never become more powerful than the player can. You’ll lose thralls this way and you’ll still have to be proactive in providing for your base. Require food and water for them for survival as well as a place to sleep. The more thralls you have to do the work, the more management is demanded of the player to make sure it runs smoothly.
Endgame is your boss farming, dungeoning, and raiding. Thralls should again be instrumental in this, but as secondary characters to the player hero. Give them siege engines they can construct and fire. Have them properly man the walls. Attacking a player base shouldn’t be a matter of offline orb throwing after a week of farming. Thrall defense should be a more effective defense than honeycombing a box. Fortifications in antiquity were built the way they were for a reason and the most effective defense should mimic those reasons in game. At the same time thrall defenders should go down without the need to cheese acid and poison arrows or to box them in with walls of your own.
Long story short a lot more needs to be addressed than just thrall hit points and damage output if the player is suppose to be the “Hero”.
Honestly, there is a lot of potential, but I think it’s too late to implement anything of merit. Best to take note for a sequel at this point. Currently thralls won’t amount to actual engaging gameplay, and probably won’t even with more patch iterations and PvP will stay the survival standard of offline raiding and animation exploitation.