Can attest to Blaz feeling out of his depth in some maps, especially those that are slaughter-heavy. Due to his melee-centric design, his melee attacks don't feel adequate in dealing with huge hordes of enemies (think Okuplok, Death in Excess, Rush). He lacks the power and AoE needed to have a similar impact that the rocket launcher and BFG does.
These days I prefer to play on the Knave difficulty for a more casual playthrough, and somehow it's still quite easy for Blaz to be overwhelmed by a horde.