If you aren't caught up with Maul: Shadow Lord, there won't be spoilers, but suffice to say that some have noticed or argued for inconsistent-seeming skill levels across different fights for the same Inquisitors. Without delving too much into debate over seeming problems of inconsistency, I think there is solid in-universe evidence and reasoning for them being kept somewhat on the weaker side, deliberately.
It's an anti-coup measure, to start. Dark emotions are a must, of course, but Sith techniques for seeking and gaining power in the Force are on another level.
This is reflected in the name! Using another iconic title for contrast, they are Inquisitors, not Terminators. Their core function is to investigate, track, and confirm the presence of Jedi - or Maul - so that Vader isn't wasting his time. Vader is the "Terminator" of the Empire.
I'm sure they can be hunter-killers for small game like a lost, frightened Padawan - those not truly worth Vader's time. (And yet a determined Padawan or two has defeated an Inquisitor or two.) And I certainly don't mean "Inquisitors were intended to be incapable of killing Jedi".
They are still trained to be a genuine threat to Jedi, including in combat. But not a sure knockout punch. Again, that's Vader, if the Inquisitors can't handle it. And Sidious/Vader expect for that to happen fairly often.
It's already well-recognized that infighting is encouraged and Vader's favor is paramount. This too, helps prevent a coup. This would also explain why the Emperor generally (Trilla excepted) preferred aliens in the Inquisitorius. An alien has far less hope of seizing control of a human-supremacist Empire.
So I think there is good supporting evidence that the Inquisitors were most often "nerfed" to some moderate degree, by design. In classic Imperial fashion, they often looked to technology - armor, spinning lightsabers - or even intimidating masks for an edge against Jedi.
On a final note that hopefully turns my ramble into an "opened-up-for-questions", I wonder just how much of exception to this the Grand Inquisitor was, in power and skill he was allowed to amass. What do you think?