Playing double weapons is a tricky business, and a well played single weapon is better than 2 poorly played. This is because it is much easier to get trapped or tied up with 2 weapons - You have to pay attention to which is over and which is under when you strike, and which options are better and worse from each position (some responses are very difficult to do if the side that needs to react is blocked by the other weapon).
Also, it is far easier to injure yourself with 2 weapons than one, it is harder to keep track of 2 edges, and the pretzeling problem makes the possibility of cutting yourself much greater.
That said, 2 weapons wielded well are easily superior to one. However .... to be superior they need to work in concert ... not doing the same thing, but doing complimentary things - For instance one opening a line and the other striking in the same moment, one faking whilst the other cuts, or one recycling/blocking whilst the other strikes.
These different 'jobs' that occur at the same time, turn out to be difficult to pull off due to our in-built physiology which leads to a tendency to keep a grip with the dominant hand even when the non dominant is being used as the primary. When one gets excited, it turns out that relaxing the grip on only one hand is very hard to do, especially if one gets caught off guard in some way, or if the 'emotional content' ramps up.
Most commonly if this happens, both weapons start to do exactly the same, rigid, thing, or the non dominant hand becomes completely inactive, usually gripped close to the body, or held in a single position, whilst the other moves as though the second does not exist.
This is particularly a problem with 2 handed weapons like the staff or cane, where the hands need to switch, and move along the length of the weapon, shortening and lengthening range, utilizing both ends for hitting, switching the power vector from down to up, inserting pokes between the strikes etc.
I know I learned to paint with my left hand by engaging the right hand in the same movement as the left, which seemed to make it easier as now the non dominant was following the dominant ... but I never thought about the reverse - NOT doing the same thing but learning how to do different things with both hand at the same time.
Consciously alternating relaxing the hands, keeping both in my mind at the same
time, was one of the most challenging parts of 2 handed weapons practice, and is still hard to maintain when things get exciting.
Here is an article about unintended discharges from firearms which is related.
PS: I would add that in single handed sword use, the 'live' hand, or hand
not holding the weapon, has a tendency to suffer from inaction, so double weapon is
the place to learn how to resurrect the live hand and it's tendency to
forget it has a life of it's own.