Several factors come into play the moment the passenger chooses what plane to fly. CI, RI, day flight or redeye, and also pricing (but not to the extent you think it does).
In a hypothetical route where the demand is 300, and three airlines fly one once per day, if all those factors above are the same for each airline, the demand will be allocated in equal parts to each flight. That is, a 100 pax per flight.
So, if you have an A321 , you would barely have an LF of above 50%. If the other two airlines have Embraer 195s, they would be close to 95% LF. That's how some of the mechanics in this game work.
Also, discounting below 20% is futile. LF won't rise the amount you expect it would, and your revenue will be down hard. I recommend never discount tickets. At the very least, hold them to the standard pricing, and raise the prices where your LF is 80-90%.