So up front i want to say i enjoy using the thunder hammer, and balance wise it is slightly underwhelming but i think its not in that bad of a place balance wise. It really isnt as different from the eviscerator as many people probably see it.
However, i do feel it doesnt quite fit a role that the fandom will probably percieve it should fill and the 40k purists are going to be disapointed with it.
The thinder hammer in general in the lore is a shock and awe weapon, its supposed to cause a scene when you swing it. It is after all a softball thick light saber … yeah the thunder hammer doesnt actually “Thonk” things to death the explosion comes from the power field evaporating the matter that comes in contact with it, and because thunder hammers are bigger two handed weapons they enjoy a stronger power field than most smaller weapons in the power weapon category.
I think you should think of the thunder hammer as a tank role weapon it should cause more havok when it attacks even if it has to come down in damage some. it already has +3 stamina making it a great blocking weapon but the problem comes from animations that are not selling the thunder hammer (it bounces back on impact it should cut like butter). and the fact that it has little effect on a crowd of enemies. I understand that it is an amazing elite eraser, maybe a little too good at that specific role. I think however if you take it into a horde that has you surrounded on all sides you will see what i mean … i have no trouble killing the horde, but it takes forever and its about picking rare repostes or shots when you have an opening … because of the wierd animations your swing speed is even more slow than it appears and recovering to block afterwards is a slow process.
It might be better to tone down its single target damage slightly, have the animations finish thier swing instead of rebounding and either have it electrocute nearby targets stunning them for no damage or maybe a pulse or two like the psychers electric staff.
A slight address to the time it takes after any swing to return to block, it is a two handed weapon and a heavier one, but war mauls were never wielded that clumsy in real life and they weren’t also metal vaporizing light saber mauls.
I think having it “optimal for elites” is still a great place for it but i think its a little too specialized right now and fans of the series will probably reject the weapon in its current state.
Also an interesting side note, there is a far more common weapon similar to what you have in the game called ashock maul, which DOES NOT have a power field it is a combination mace and taser combo that the arbitas generally use with a combat shield that could be a great fit for the preacher giving them a shield (away to tank the deamonhost if theres no ogryn) and the ability to stun opponents with a faster one handed weapon group.