First of all, I am sorry if this has been discussed before.
That's what the search function is for! Surface landscapes on Oceania planets is a known bug:
As to the possible types of Oceania, some may simply be terrestrials like Earth but with more Ocean (your type a), and others may be completely water worlds, with transitions to high-pressure ices at lower levels (type b). From above these may superficially look the same, but some properties like bulk density will be different. I don't know if SE yet distinguishes the different types, but it is supposed to render them as a terrestrial sized body with a deep ocean. Some may also have ice caps or a frozen surface like Europa, depending on distance, rotation, and greenhouse effect.