Why reconstruction could not easily make Lexington a fast battleship

Could Lexington's firepower and speed compensate for weak armor, and could the class later become a good carrier escort?

Its speed and guns supported useful battlecruiser and escort roles, but its basic protection and subdivision made conversion into a balanced fast battleship impractical.

There was a large difference between evolving a well-protected design toward fast-battleship standards and rebuilding a lightly subdivided battlecruiser. Hood approached the transition but did not fully reach it. An improved G3 might plausibly have developed into a balanced fast battleship because it began from a stronger protective basis. A Lexington would require such extensive internal change that constructing a new ship would be faster, easier, and cheaper.