Tactics for Rampart.

I agree – in this respect, they are similar to Dungeon.
After building the 3rd level of the guild, there is a temptation to build the 4th level instead of upgrading the dragons.

But no, they are very different from Dungeon. Red dragons are much more expensive to build than green ones. But Dungeon is actually cheaper than gold (if you consider the gold cost, which is usually scarce). And by the way, if you play as a Fortress, the desire to upgrade the guild drops sharply.