When it comes to the usefulness of the weapons added in OWB, I think they were great, only downside to them was trying to use them against enemies in the Big Empty. I even took a pulse gun with me to help starting out since I knew there would be robots....suffice it to say....it svcked, even though in the Mojave no robot I faced stood much chance against it, I guess the robots of the Big Empty are that amazing.
I'm going to check this in the GECK later, but based on observation of firing various weapons at a Mk4b Roboscorp it appears that the mechanical critters in OWB have rather large HP pools. This was seemingly confirmed after I found Elijah's Jury-Rigged Tesla Cannon, loaded it with MC ECPs, and plugged away at yet another such scorp, as it took 4 shots to kill it. Note that my EW skill on this character is only about 70, so the cannon was not doing as much damage as it's actually capable of; it would probably have taken 3 shots otherwise. Still, that's a 300ish-point HP pool to chew through, DT notwithstanding.
Them being HP sinks would explain why, even with the 'Gabe's Bark' tone installed, the sonic Emitter took several shots to down one scorp, given that I know from trying that the Pulse Gun will almost one-shot a normal Sentry Bot and that the Emitter is essentially a variant thereof. For what it's worth, with the Roboscorp tone installed it was taking 3-4 shots depending on model.
Just to cover all the bases: the character in question went in at L29, so it's possible he was facing the top-end variants off the leveled lists. I have not (obviously) yet tested to see if a lower-level character has an easier time under the same circumstances, although it wouldn't surprise me if that were the case.