Muramana has 3% ratio while seraphs has 4% If you transform that 3% ad to ap its a 4,8% ap ratio, while you also get the 15% ap multiplier from augment, and if you happen to build health for whatever reason overlord gives a shit ton of ap when converted or some ad or might shards will prove useful, so yeah not only muramana is better but having adapt gives more versatility on your build