I *think* you'll find the f100 comes out very close to the f70, for instance.
If I'm not mistaken, the F100 and F70 have the same engines/fuel burn, but the F100 has 50% more seats.
The other thing that might be illuminating is to put in some bigger planes, but assume they only seat 80. Like a 717, an a320, etc. If the operating costs are very similar, then you may as well use the bigger plane and just have empty seats on some routes. I *think* you'll find the f100 comes out very close to the f70, for instance.
This is basically what I was trying to say with using a fixed number for pax
Also, while it may seem jets would be a waste on shorter routes, they also attract more passengers. If you had the option of flying a noisy turboprop or a quieter jet, which would you take? Business class pax also like the jets. In regards to fuel burn, don't forget that props fly about half as fast as jets. So a jet with 2000 kg/hr fuel burn is approximately the same as a prop flying 1000 kg/hr, although on shorter routes we're only talking about a matter of 5-15 minutes in flight time.
As for my all-CRJ airline, my longest route was ~800 miles on dense routes and I'd say 90%+ of my routes were under 500nm (routemap attached). I had 151 CRJ at the end of the game with bases at CVG, STL, MCI, and MSP in that order. My net profit margin with 4 bases was between 10-15%, which is strong. The biggest downside was paying for so many damn slots. If you go with 2x70 seats versus 1x100 seats on your routes, don't forget you are buying double the slots, which can cost many millions.
Speaking of slots, you should make sure you can convert your existing routes to whatever plane you end up with. If you have to shift schedules then you'll end up paying AGAIN for slots, which can cost a pretty penny and you may also have to bump routes from your existing schedule depending on what kind of cushion you have built in. One of the reasons I was so successful with my CRJ airline is I could swap out the schedules easily without extra slot costs. I could start with a 50 seat CRJ, convert to a 70 seater, then a 90 seater without dealing with scheduling conflicts. Thus, as demand grew over time and my route image went up, I could respond to the new market conditions rather easily by putting more seats on the route. You have this flexibility with the F70/100, the CRJ fleet, and the E-jets. Not so much with the others.
So long story short--you need to look beyond the spreadsheet to determine which aircraft is best for you
Flying regional jets is tough and every penny counts, especially if you are in a smaller airport with limited demand.