The big one was its complete lack of mobility abilities or ranged attacks, so a party with overland flight could attack it pretty much with impunity. Iirc that was most commonly paired with shrinking a bunch of boulders, carrying them up with you, then dropping them right as the shrinking spell expired. This is all from memory 15 years ago though so details could be a bit sketchy.

I haven’t played Stoneburner yet, but I ran a 10 session campaign of Tales of the Burned Stones (the free fantasy version released as a reward from the Stoneburner Kickstarter), and it was super fun! If you get a chance I highly recommend bumping Stoneburner up in your queue.