Are there any hierarchies in mathematics that aren't like this? It seems like most hierarchies are constructed such that going up one "level" expands your scope

Are there any hierarchies in mathematics that aren't like this? It seems like most hierarchies are constructed such that going up one "level" expands your scope so much that the previous rung looks like a drop of water in the ocean. Examples include, for example: the Chomsky hierarchy of languages, where most context-free languages are not regular; Turing computability/solvability; and so on.