To my (limited) knowledge, one has to put the nominalizer
の/ん between a verb and a copula. However, when I was learning the usage of である, the written, literary copula, I read that
であろう can follow a verb directly. That was when I realized that
だろう/でしょう works in the same fashion.
I understand that の/ん is optional context-wise in this case, but how come the so-called volitional form does not need to have the preceding verb nominalized?