I find snipers bullets very strong but they are weak against humans. I want to have one of the strongest garison of the server, when I sit nobody take me off. I don't like the undead thing because they still die, and that's a lot of ressources lost. I'll probably go to human then, because they all go to hospital too.
I play Dwarf at Castle Level 40. I have a few thoughts, but first I want to address your comment on Undead. Undead units can get a 90% (someone confirm this, they switched it around a bit, it may be 80% now) resurrection rate with research, and it is an instant revive. That means it will take five separate attacks to fully kill one stack, as they will revive immediately and be placed back onto the wall. If you spend all your mithril building gold scorpions, all your crystal building gold spiders, and all your diamonds on mummies or stalkers, you will have a very difficult wall to beat with instantly reviving units. Plus add in the desert bonus, and the fact that Lich hard counter Humans, who seem to be the best end game siege class, and you are even stronger. The gold scorpions will also melt the Dwarf silver mech frontline, so you are relatively safe from dwarves too.
On to Dwarves. Dwarf has a strong garrison, the biggest issue being that our most viable tanking unit, mechs, permanently die. But, what else are you going to spend mithril on? At max level, all your mithril should be dumped into gold mechs for your wall anyways. You have to look at it as an overall investment in securing your RSS to continue building units that don't die. But, if you get hit hard and lose all your mechs, it will take a very long time to rebuild them, probably weeks. You can add engineers, but they are subpar in every respect. The other issue with Dwarf garrisons is what you pointed out, sharpshooters don't do well against troops that have more units per stack when they have high evade chance. They fire relatively slow and will hit one troop at a time, so they will never shine against a full stack of gold swords, especially when they have a 30% evade chance. But, a well researched stack of blasters can clear out swords relatively well, assuming the swords are not god tier in research with a backline of gold healers that are also god tier in research. That combo is pretty much unbeatable.
Also, keep in mind that no wall is safe anymore. We have seen high level research players use Rank 13 Bronze units to clear out Rank 13 gold walls (Lich v Human). We have seen well researched human players field four gold swords with two gold healers and silver archers to clear out full gold garrisons with minimal losses (90% injury rate with King).
The end game balance is completely out of whack, so you should not assume you will be safe long term with any race. Dwarf is as viable as any of the other races, they just have the biggest penalty if they get a full clear.