They aren't really so closely related as you are implying, since bitcoin is a trustlessly decentralized system. At present every participant needs to be able to validate the entire chain in order to be certain that their copy of the ledger state is correct, and miners need to be able to incrementally validate blocks in particularly short timeframes or else.
It is possible for a decentralized system like bitcoin to scale via distribution in a way that introduces minimal trust, for example by probabilistic validation and distribution of fraud proofs. However changes to bitcoin consensus rules (mostly soft-forks) are required in order to make this possible.
I don't want to discourage thinking about scaling bitcoin in such ways, as it is a viable medium term proposal. However right now with the bitcoin that exists today parallel distribution and decentralization are at odds with each other.