honestly the easiest way to combat botting in an HNM situation is to make the mob have mechanics like that of Dark Ixion or Sandworm in FFXI. They had random(well kinda random) spawn conditons where they even changed actual zones every spawn. Yes bots still worked with those but if you didnt have a competent LS you still were not going to claim it. I would say build on those mechanics making them more random as in no patterns at all or at least enough patterns that it wont repeat for at least a week.
For people who did not play XI i will summarize how Sandworm and DI generally worked:
Sandworm: Could spawn in iirc 9 different zones with about 2-3 different areas in each zone. The zone of spawn was usually to large for one person to be able to stand still and notice the spawn so you had to run around searching. It also had no window intervals like that of Fafnir/Behe.. meaning it could spawn at anytime of the random spawn period which was 20-24 hours.
Dark Ixion: pretty much works the same except if there was a campaign (major NPC battle event; kinda like behest) it would run out of the zone and into another zone where no battle is taking place. Yo also needed a special throwing item to even claim it. Once claimed it pretty much killed anyone solo unless you were extremely skilled and geared.. honestly there was no one who could claim it and hold it for more then about 15-30s other then the best geared Paladins.
I think the way those mobs work are the best way to implement HNMs into FFXIV with more tweaking and building on the mechanics to fit the game and make it more fair.
The simple fact is that no matter what a developer does there will always be a bot. and i think people blame the devs way to much thinking they are not doing their job when its not the case. If a game uses a mouse and keyboard AT ALL to input commands there will be a bot always. no if ands or buts because a bot simply presses keys for u. So instead of saying no to HNM's period because of bot wars just use mechanics that aren't able to be predicted.
Also if the FFXI HNM ways dont fit the playerbase make it something like this :
-Said HNM has a domain where he rules
-The domain is NOT instanced but rather have it where u need special qualifications to enter you group whether it be quest or farming tokens ( like headresses for Garuda in 1.0)
- The domain is a VERY hard place to navigate and get through meaning mobs are hard.. mini bosses are present before you get to the main boss.
-The Main HNM boss can move to anywhere in its domain.. its kinda dumb to call something Behemoths dominion and he only pops in the same spot every time not much of a dominion.
-The HNM has a random respawn timer or lottery spawn like the mechanics of FFXI. Make the Respawn timer like 6 hours with a lottery spawn from killing the mini bosses and it can take up to 12 hours to spawn starting at 6 hours. Can adjust these numbers to 2-4 3-6 or whatever to fit the player base.
- The most important thing is to make this content difficult as to not make it outdated because of ease of access to the gear. Make it take at least 1-2 hours to even reach the HNM with a full alliance of people. (See. Dynamis Lord or Kirin from FFXI)
and thats my wall of text for HNMs