There is nothing wrong with the friction model, and the F-5's ground handling is accurate. Due to the F-5's short wing and clean aerodynamic design, it as a high approach speed. The aircraft also has very narrow tires, and does not have an anti-skid system, meaning if you lock the brakes, it's just going to slide. That is why the F-5 was fitted with a chute to aid in its stopping distance. The T-38 is the same, except without the chute. Because of the T-38's incredibly long stopping distance, Talon Pilots in the Air Force need special permission to land at any airfield less than 8,000 feet in length.
You're just used to aircraft with slower landing speeds, more effective air-brakes, and wheel anti-skid systems. The F-5 has none of those, so you must plan your landings carefully and use subtle braking. Also, keeping the nose up on landing role (aerodynamic braking) helps shorten your landing distance.
