When it is 5:1 you need a fast plane to survive. That's how I manage. I can't create angles like BigR and don't have the gunnery of most here, so I survive by hoarding energy and knowing when to bug.
There are different situations for different planes. If you only fly one plane (there's nothing wrong with that), you will die more often in situations when you should not have not have picked that plane.
Situation 1
You and/or a couple of wing men fly super fast planes into a big hoard of 20 enemies agaisnt the odds, who are attacking your base. Yes this is the time to fly a 190D, P51D, Temp, 262, TA152. You want to be high and fast and quick to scatter them out. Roll from a back base. You want to be able to allow friendlies at the base you are defending to be able to roll and break the cap. Quick shot kills and Diving away is extremely important, and most planes won't catch you. This is how you bust up a big hoard. Flying planes such as a Ki84 or 109 in this case would not be sufficient as you would get ganged and picked rather quickly not being able to dive away.
Also the best planes for hunting bombers.
Situation 2
There is a furball on the map but your side is pushing them back. You need a plane that is a good mid alt fighter but has some gas to reach their base and can maneuver. These planes include 109s, f4us, Niks, P38, Ki61, c205, Fm2, F6F, 190A5, P51 and P47, a wide variety as you can see. These planes are good at high and low alts, can generally dive well, can maneuver better than most in desperate situations, and are generally quick. You don't necessarily need a super BnZer like above, because you will end up getting caught low and cannot maneuver like a mid alt fighter. BnZers in this case will spend more time missing shots and rolling off, and running away from Turners, than getting kills. Defensive planes, next situation, don't dive well and have poor gas range. They work but normally end up getting too mixed up with the lower cons and get ganged, hard to escape the fight in defensive planes.
Situation 3
So you see a furball at your base and your team is holding ground and you have a chance to roll! You need a plane that is quick and agile to get right into the fight. This is when you roll a Ki84 (especially agaisnt CV planes), spits, La7-5, Yak, A6M, Ki43, Hurricane, sometimes K4, ect. These planes can lift up quickly, gain speed quickly, can dip dodge and duck very quickly from the fighters dropping on them. The key in these planes is to be quick with quick shots before the higher ones drop in. You can easily maneuver around them and get the overshoot if they try to turn with you. These turny stall planes will get the pickers to lose their steam trying to line up shots on you. This is how to sucker the higher ones down. Rolling a P51, TA152, P47, P38, 190D, Temp, would be a very poor choice in this kind of situation. If this is the only plane you know how to fly. You are going to have a hard time and die more often than not. You aren't going to have a good time, just like in the other situations.
By chosing a plane that is more suitable for situation. You will probably have more fun, get more kills, and learn the game better.
All I am saying is that if you only chose to fly one plane, and you fly it in situations that are not suitable for the plane type. You will have a higher rate of deaths overall and get a lower K/S and K/D most of the time.