I think it's debatable actually. The attack bonus from forts doesn't apply to staff units, nor does the attack from charge. The defense boost and the 1hp/lvl trait are nice, but they shouldn't really be getting hit much anyway. Conclaves can get an extra essence which can be a training bonus. So it's a question of is +6 defense, +2 lvls, some accuracy, and impulsive (or 1/hp/lv) better than +6 fire attack, +6 hit points, +1 initiative, and +1 defense? I think it's close, close enough in fact that I sometimes even play without forts and just train all my units at a 6 essence conclave (4 base, +1 scrying pool, +1 oracle). Means more research and mana, more refinements and more of that +1 lvl to all trained units spell if I want.