  We establish \textit{structured quantitative almost reducibility}, tailored
for analytic quasiperiodic $SL(2,\mathbb{R})$-cocycles, which effectively
addresses the challenge of infinitely many \textit{normal frequency}
resonances. This method paves the way for optimal arithmetic reducibility
results for such cocycles, thereby resolving Jitomirskaya's conjecture. From a
spectral perspective, it leads to optimal arithmetic Anderson localization for
a class of quasiperiodic long-range operators on higher-dimensional lattices.
In particular, using structured quantitative almost reducibility, we establish
a sharp quantitative version of Aubry duality, enabling us to uncover new
spectral insights for almost Mathieu operators with Diophantine frequencies.
For example, we precisely determine the exponential decay rate of spectral gaps
in non-critical cases, thus addressing a question raised by Goldstein.
Additionally, we reveal the optimal asymptotic growth of extended
eigenfunctions for subcritical almost Mathieu operators.
