  Due to the inclination for forward gauge radiation, lepton colliders beyond a
few TeV are effectively electroweak (EW) boson colliders, suggesting the
treatment of EW bosons as constituents of high-energy leptons. In the context
of a muon collider, we revisit the validity of $W$ and $Z$ parton distribution
functions (PDFs) at leading order in $2\to n$ process. We systematically
investigate universal and quasi-universal power-law and logarithmic corrections
that arise when deriving (polarized) weak boson PDFs in the collinear limit. We
go on to survey a multitude of $2\to n$ processes at $\sqrt{s}=2-30$ TeV via
polarized and unpolarized EW boson fusion/scattering. To conduct this study, we
report a public implementation of the Effective $W/Z$ and Weizs\"acker-Williams
Approximations, which we collectively call the Effective Vector Boson
Approximation, into the Monte Carlo event generator
\texttt{MadGraph5\_aMC@NLO}. This implementation lays the groundwork for
developing matrix-element matching prescriptions involving EW parton showers
and renormalized EW PDFs. To further with this agenda, we give recommendations
on using $W/Z$ PDFs.
