  We study the growth of the local $L^2$-norms of the unitary Eisenstein series
for reductive groups over number fields, in terms of their parameters. We
derive a \emph{poly-logarithmic} bound on an average, for a large class of
reductive groups. The method is based on Arthur's development of the spectral
side of the trace formula, and ideas of Finis, Lapid, and M\"uller. As
applications of our method, we prove the optimal lifting property for
$\mathrm{SL}_n(\mathbb{Z}/q\mathbb{Z})$ for square-free $q$, as well as the
Sarnak--Xue counting property for the principal congruence subgroup of
$\mathrm{SL}_n(\mathbb{Z})$ of square-free level. This makes the recent results
of Assing--Blomer unconditional.
