BU's fundamental purpose is Semi-Unrestricted block building (accelerates network centralization).
CORE's fundamental purpose is Semi-Restricted block building (preserves network decentralization).
Bigger blocks tend toward network centralisation, but decentralises the user base (more people can afford to send bitcoin).
Small blocks allow greater network decentralisation, but centralises the user base (only a few big actors can afford to send bitcoin).
How decentralised is LN?
It would seem the former of these two options was envisiged by the creator at the time. Nodes centralising around well connected mining nodes and bitcoin service providers, and users using SPV wallets.