Magento 2's layout XML system is the backbone of every page render. It controls which blocks get instantiated, which templates get rendered, and how the page tree is assembled before PHP hands off output to the browser. It's also one of the most overlooked performance vectors in the platform. Unlike database queries or JavaScript bundles, layout XML overhead is invisible in standard monitoring. You won't see it in a slow query log. It won't show up as a large network request. It hides inside TTFB — Time to First Byte — silently burning CPU cycles while your server assembles the block tree. This guide dives deep into Magento 2 layout XML performance: how to audit what's being rendered, how to remove what isn't needed, and how to use caching and lazy rendering to get the most out of the system.…