i didn't say it's hard to make, I just said you won't make as much money compare to the larger aircraft like erj and 737/md90 etc.
let's say you have a route that has 170 demand. it will take 3* dash 8 frequency to fill it. While larger jet like 737 can do it in one pass.
yes you may save on fuel, but flying a slower aircraft means it takes up time.. and time = lease expense, not to mention you will need to fly 3 times... = crew, slot, maintience
prop also does not do as well if you fly long range, reason above.
Like i suggested, get a mentor request out, I am pretty certain what your mistake is, but can't confirm until one look at your airline schedule.