It's true the gameplay loop starts to break down at around this stage due to gold hoarding and how the power scaling doesn't account for the fact that you can just run several gold mines at once, or maybe it does and you're just expected to have hoards of followers die per invader.
Since I started with the idea of just creating a spike corridor, I figured out quickly that any invader will die or come close to dying before they even encounter anyone. (You might want to consider starting another save to try this)
For whatever reason, all the status bars, in this version, are fixed at 100, and 4 level 5 spike traps do a fixed 26 damage (you do the math on that one). With a graveyard and an alter, you have the option to revive any of them and now you have a high levelled zombie.
If you would rather have high levelled living followers or don't want to put in a spike trap corridor, then:
- Use Nail Bombs! Nail Bombs have the equally amazing property of having fixed damage, just chucking 7 Nail Bombs at someone(7 x 15 = 105 damage) will always take them down to 0 health. Unlike in monster capture games, a character at 0 health only dies once you end your turn, which means you can either use the capture ability or Shackles.
- Send followers out to capture others. Whether you managed to capture a high levelled follower, or they somehow died, you can always send them back out in search for others to bring back (yes I mean sending zombies out, not just a corpse). Followers will always capture others around their level.
This all being said, high levels become a bit pointless since combat just turns into sticking sharp objects into anyone until they either submit or die, but it at least gives you the freedom of keeping whoever you want despite their combat ability.