per the arelith wiki Bard page: [https://wiki.nwnarelith.com/Bard]
Bard receives a +3 bonus in defense vs. Dispels if they have at least 21+ bard and they do not have the following classes: Paladin, Blackguard, Zhentarim Enforcer, Harper Paragon, Cleric, or Harbinger.
paladin and Blackguard, i believe, are on this list because of their access to Divine Grace [https://wiki.nwnarelith.com/Divine_Grace] alongside divine Shield and divine Might.
however, from my testing of this, Liberator [Found at https://wiki.nwnarelith.com/Liberator] is unbothered by the above list, and seems overlooked. If this is intentional, nothing needs to be changed, but presently it is possible to be 27 Bard / 3 Liberator and have full CL against Dispels while gaining the bonus of Divine Grace / divine Shield.