Cardiff-Anglesey had 825 passengers in September, a month when people were largely back from summer holidays and normal work had resumed
September had 22 weekdays, so allowing for 2 round trips per weekday there were, on average, less than 10 pax per flight.
Yes some flights will be busier than others, but even with a 19 seat aircraft, the load factor was around 49 %
I would want a good reason to be very evident before even thinking about an aircraft with significantly more than 19 seats on this route.