  We establish Monod's isomorphism conjecture in degree-three bounded
cohomology for every complex simple Lie group of classical type. Our main
ingredient is a bounded-cohomological stability theorem with an optimal range
in degree three that we bootstrap from previous stability results by the author
and Hartnick. The bootstrapping procedure relies on the occurrence in our
setting of a variant of the recently observed phenomenon of secondary stability
in the sense of Galatius--Kupers--Randal-Williams.
