With centralized L2/L3s, a company is the block builder/proposer (captures priority fees) and the sequencer (captures sequencing fees). If only the sequencer is decentralized, is the rollup *really* decentralized, if most of the economics in the form of priority fees still go to a central party?

This is why community-owned rollups like @metabased are where things are inevitably headed. Decentralization of not just the tech but the full governance and economics which not only leads to more prosperous networks, but as a result, a more resilient, sustainable, and scalable ones.