This proposal has now been substantially revised. The new version + discussion and PR are here:
To address your question from back then: ERC-6551 creates smart contract accounts owned by NFTs. It has no concept of weighted constituents, proportional withdrawal, or composition management. The overlap is only that both involve NFTs in some capacity. The original draft used ERC-721 for ownership, which may have created that impression. The revised spec uses ERC-173 for ownership instead.
The comparison to TokenSets is more relevant. TokenSets, Index Coop, dHEDGE, and similar protocols all implement weighted basket mechanics, but each with a different interface. That is exactly the problem this standard addresses, not the concept of baskets (which clearly exists), but a common interface so that wallets, aggregators, and indexers can support any conforming basket without protocol-specific integration.
The revised spec includes a detailed comparison to ERC-4626 and ERC-7575 in the Rationale section.