In blockchain systems operating under the Proof-of-Stake (PoS) consensus mechanism, fairness in transaction processing is essential to preserving decentralization and maintaining user trust. However, with the emergence of Maximal Extractable Value (MEV), concerns about economic centralization and content manipulation have intensified. To address these vulnerabilities, the Ethereum community has introduced Proposer Builder Separation (PBS), which separates block construction from block proposal. Later, enshrined Proposer Builder Separation (ePBS) was also proposed in EIP-7732, which embeds PBS directly into the Ethereum consensus layer. Our work identifies key limitations of ePBS by developing a formal framework that combines mathematical analysis and agent-based simulations to evaluate its auction-based block-building mechanism, with particular emphasis on MEV dynamics. Our results reveal that, although ePBS redistributes responsibilities between builders and proposers, it significantly amplifies profit and content centralization: the Gini coefficient for profits rises from 0.1749 under standard PoS without ePBS to 0.8358 under ePBS. This sharp increase indicates that a small number of efficient builders capture most value via MEV-driven auctions. Moreover, 95.4% of the block value is rewarded to proposers in ePBS, revealing a strong economic bias despite their limited role in block assembly. These findings highlight that ePBS exacerbates incentives for builders to adopt aggressive MEV strategies, suggesting the need for future research into mechanism designs that better balance decentralization, fairness, and MEV mitigation.

翻译：在基于权益证明共识机制运行的区块链系统中，交易处理的公平性对于维护去中心化和保持用户信任至关重要。然而，随着最大可提取价值的出现，对经济中心化和内容操纵的担忧日益加剧。为应对这些潜在风险，以太坊社区提出了提议者-建造者分离方案，该方案将区块构建与区块提议职能相分离。随后，EIP-7732提案中进一步提出了内嵌式提议者-建造者分离机制，将提议者-建造者分离直接嵌入以太坊共识层。本研究通过建立融合数学分析与基于智能体仿真的形式化框架，评估其基于拍卖的区块构建机制，特别关注最大可提取价值的动态特征，从而揭示内嵌式提议者-建造者分离机制的关键局限性。研究结果表明，尽管内嵌式提议者-建造者分离机制重新分配了建造者与提议者之间的职责，却显著加剧了利润与内容的集中化：利润基尼系数从无内嵌式提议者-建造者分离机制的标准权益证明机制下的0.1749上升至内嵌式提议者-建造者分离机制下的0.8358。这一急剧增长表明少数高效建造者通过最大可提取价值驱动的拍卖捕获了大部分价值。此外，内嵌式提议者-建造者分离机制中95.4%的区块价值奖励分配给了提议者，这揭示出尽管提议者在区块组装过程中作用有限，却存在强烈的经济偏向性。这些发现表明，内嵌式提议者-建造者分离机制加剧了建造者采用激进最大可提取价值策略的动机，提示未来需要研究能更好平衡去中心化、公平性与最大可提取价值缓和的机制设计。