EXPLANATION CHAPTER, skip if you want.

So the reason why Emrys, Le-Fay, and Pendragon rings are different, my thinking is since Merlin modeled the order of merlin later the wizengamot after arthurs knights of the round table and british nobility, the 4 founders even though older, wouldn't have considered themselfs lords or held any power in whatever government was around for wizards back then, so once merlin made a government and included the 4 founders, they just used their crests for rings while pendragon was the first 'muggle' lord on a magical governing body since it took place on his kingdoms land, Le-Fay since Morgana was trying to take over and was originally merlins student would have been apart of the order of merlin before she well did the more corrupted things, and merlin since he was a first generation wizard, so the founders used their crests for their rings, and everyone else just followed it since it was easiest, also I didn't wanna look more stuff up so its my excuse. As for plot holes, when gringotts was formed, merlin used his magic to help them out and as such they gave him a vault, as for how the founders got their, not sure but im using my powers to make it so gringotts was formed slightly earlier and the founders died slightly later. Make sure to let me know if you have any ideas or idk anything you wanna say or ask.