If the only thing that mattered was the length of the tail, every airplane, fullscale or mode, would have long tails. Maybe. Maybe not.

Problem is that length is not even the most important detail (pun intended).

Take the P40 Warhawk for example. Remember that most airplanes have both a horizontal and vertical tail. Length and area matter for both.

The Warhawk as it was designed, approved, and produced originally had a problem. It was unstable in yaw. They solved the problem two ways. First solution was to add area aft. That worked. There is a strong argument about length being the only solution. They started extending the fuselage in the middle of the P40F series run and didn't need the extra area. And they didn't move the horizontal tail back when they moved the rudder back.

Had the vertical tail had enough area, none of that would have happened. The Warhawk would have been just as smooth with a shorter tail.

Balance, weight, strength, durability and a few more things go along with aerodynamics when designers are juggling the numbers trying to fit the mission requirements. If you've ever used and studied the CG applications you can see how there are way more than one thing that matters. The Warhawk horizontal tail could have been moved aft too but if it hadn't been downsized could have upset the balance. But why change something that was working ok.