Having listed his shortcomings, I want to have a look at what he CAN do so as to work out where he might have mileage. The Ancient costs roughly as much as 2 BGVs and has minimal damage output of his own. 2 BGVS get 6 attacks (8 on the charge) hitting on 3s before buffs and Chapter bonuses. So the question then becomes, how many BGVs would the Ancient need to buff before it becomes better value than just buying 2 more BGVs?
6 attacks will generate 4 hits with most Chapters. A +1 to-Hit bonus will generate 1 extra hit for every 6 attacks on average so you will need to be buffing 24 attacks for the Ancient to break even. This means an Ancient would need to have 8 BGVs in their aura for the buffs to equal 2 extra models in the squad. So the ancient will only be superior if you are running 2 5-man squads or more.
So it looks like the wisdom of the Internet is spot on. It is hard to get enough BGVs into the Ancient's aura to be worthwhile and once you start taking casualties, you would quickly end up being better off with more bodies. The Ancient's value falls even further in Chapters like Space Wolves and Dark Angels as the bonus does not stack with their Chapter Traits. Sadly it looks like the best thing for this guy is conversion fodder.

Can anyone think of any possible use cases I have failed to consider? Do any Chapters have Relic banners that make this guy competitive (moreso than other Ancients)?
Edited by Karhedron, 21 November 2021 - 10:24 PM.