You can't blame the writers for everything. Beltran and Montgomery got their episodes in which they could shine and Fortunate Son and horizon were great ... accept for Montgomery's performance.
In the case of "Fortunate Son," it really was the case of the writing or perhaps even the directing. You can say that Montgomery was miscast as Mayweather, but the character really had been gutted of anything really interesting perhaps even before "Broken Bow" was filmed and what was left wasn't much for Montgomery to work with (a good character has to first be
a character, IMO).
I've seen Montgomery in episodes of Single Ladies
and the difference was like night and day compared to ENT, but then the characters he was playing were far more interesting and had more of a presence than Mayweather ever did.