I've got the list of drawbacks.
- Infested from inside with cultists who blend in with the normal populace of mages, festering like a tumor in their society, causing in no particular order: a reason for Connlaoth to take up arms against them; validity to Connlaoth's claim that magic is bad and thus increasing the likelihood of other nations turning against them, a constant threat to their children, their citizens, their leaders, their sense of security and safety, their social order, their pride, their image, and the very foundations of their own belief that magic is a blessing not a curse; the burden and difficulty of trying to hide these maniacs from the rest of the world while still trying to stamp them out because they cannot let the rest of the world know their lovely, socially advance society is dying from the inside out; and finally the looming possibility that should the cultists succeed, Le'raana will have a tyrannical, vile, demon-worshiping kingdom of dark mages to deal with.
- an over-reliance on magic, which has made them flippant, haughty, and disposed to extravagance and frivolity. Which in turn has lead to...
- nobility that are either decent but out of touch with the middle and peasant classes, or entitled, deceitful back-stabbers. That's when they're not conducting horribly irresponsible magical experiments that kill many people and then trying to cover it up to protect themselves. Which in turn has lead to...
- a disillusioned middle class futilely struggling against an impossible infrastructure.
- an apparently severe lag behind Connlaoth technologically, and as technology impacts every aspect of life Serendipity then suffers in every aspect of life. Nothing will remain untouched by their technological retardation. Going by only the things mentioned in this thread, that includes poorer hygiene; primitive health care (thus leading to much disease and death because mage healers are still rare and expensive); horrid roads away from the cities, hindering transportation which in turn hinders trade which in turn results in poor economies, famine, and illiteracy and a general lack of education; a piss poor military when compared with Connlaoth and Adela due to primitive weaponry, in which their only strength is a handful of mages (which are far out-numbered by regular, non-mage troops); aaaand finally abandonment of all aesthetic values outside of the cities, making the towns, villages, and rural areas dreary and hideous. (And bear in mind this is just what was brought up in the thread and doesn't include the copious amounts of absent technology we haven't even covered yet.)
- No access to iron. While falling under the encompassing umbrella of technology, this deserves special mention, as it effectively locks them in the bronze age while the rest of the world (probably even Adela, THE poster boy for lack of progress and adherence to tradition and the status quo) moves on.
That's all our drawbacks, unless I missed some.
...it seems like a wide awake nightmare for anyone but nobility or mages to live in.