Researchers specialize and as such even in a "single field" they work at very different levels of abstraction; one subfield will care about building up some novel construction from first principles and then another subfield will want to use that construction as a basic axiomatic building block and abstracting from the details. E.g. execution performance optimization of a known formula is orthogonal to developing a better formula, we want people working on both these aspects, these are going to be different people who each build on their own subfields first principles that don't overlap much with the first principles of the other researcher.
