The garrison rules are what make it controversial in my opinion, since it not only gives the enemy a potential bonus but 100% denies any additional benefits. Even if it had 2 tiers of bonuses (+2 to bravery if wholly within 12” for coalesced, add 1 to all D3 conjugation rolls for applicable heroes within 18” for starborne) plus the MW if garrisoned. Then fine, place it anywhere and have any old jerk be able to walk in. Although from a lore perspective I feel that enemy units should not be able to garrison - I picture some weird hieroglyphs on the side that only respond to Seraphon lifesource, and when touched, the stone turns into a portal which opens for your dudes. Like a Dracothion fingerprint reader. Why should Slaanesh be able to enter it? They can deface it, destroy it, etc. But to walk in and out their feet up on the furniture? That’s the epitome of lore butchery in my poor eyes.