Neonchameleon
Legend
I'm trying to work out whether you're calling Eberron a kitchen sink setting or not here. Because there is a lot of theming in Eberron - but it also explicitly says that if it exists in D&D it exists in Eberron. For that matter Sharn is another explicit kitchen sink setting where you can play most things that can reach Sharn - but there's a lot of theming in Planescape.?
It’s not a number. It’s not like, and the DM spake, saying, "Then shalt thou count to three races no more, no less. Three shall be the number thou shalt count, and the number of the races shall be three. Four races shalt thou not count, neither count thou two, excepting that thou then proceed to three. Five is right out! Once the number three, being the third number, be reached, then thou havest the proper number of races.”
“Kitchen sink” merely means that there are no real thematic (or other) restrictions on the PCs; if it’s in an official book, it’s good to go.
Which means either (a) there are two examples of official kitchen sink settings that have pretty strong theming or (b) you can play just about anything in D&D in a setting (and an official setting no less) and not have it be a kitchen sink setting.
Which means either the designation "a kitchen sink setting" is in your world either more or less meaningless or it only refers to settings that have been done badly and isn't inherent to either the game or setting.