  Recently, models of the quasar luminosity function (QLF) rooted on large
observational compilations have been produced that, unlike their predecessors,
feature a smooth evolution with time. This bypasses the need to assume an
ionizing emissivity evolution when simulating helium reionization with
observations-based QLF, thus yielding more robust constraints. We combine one
such QLF with a cosmological hydrodynamical simulation and 3D multi-frequency
radiative transfer. The simulated reionization history is consistently delayed
in comparison to most other models in the literature. The predicted
intergalactic medium temperature is larger than the observed one at $z \lesssim
3$. Through forward modeling of the He II Lyman-$\alpha$ forest, we show that
our model produces an extended helium reionization and successfully matches the
bulk of the observed effective optical depth distribution, although it
over-ionizes the Universe at $z\lesssim2.8$ as the effect of small-scale Lyman
Limit Systems not being resolved. We thoroughly characterize transmission
regions and dark gaps in He II Lyman-$\alpha$ forest sightlines. We quantify
their sensitivity to the helium reionization, opening a new avenue for further
observational studies of this epoch. Finally, we explore the implications for
helium reionization of the large number of active galactic nuclei revealed at
$z\gtrsim5$ by JWST. We find that such modifications do not affect any
observable at $z\leq4$, except in our most extreme model, indicating that the
observed abundance of high-$z$ AGNs does not bear consequences for helium
reionization.
