My dad was in the Air Force, he flew F-5's (AKA the Mig 28 in the original top gun), I have a pilot's license... but that has no real bearing on this discussion, it is only to brag and sound like an expert.
Planes have actually become slower, much slower, F-14s and F-4s, the work horses of the cold war era, were far faster jets than the current F-15, F-22 and F-35s. F-14s, the plane in the original top gun also had the capability to engage at a far longer range than almost any modern fighter, it was designed for fleet defense and air superiority. It had the ability to launch missiles from well beyond visual range, it was faster than almost anything and, by virtue of it's variable wings, more maneuverable than any fighter prior to the modern era of 'thrust vectoring' fighters. Sadly, the F-14 was phased out because of it's single use expertise, air to air domination. It lacked the ground attack ability of other planes, like the F-18, F-16 and F-15. While it was faster than all those planes and more maneuverable it lacked the multi-role capability that most modern US fighters possess.
But the biggest advancement in the last 20-30 years is in avionics. Until recently, if a pilot wanted to engage with a missile they needed to fire and keep the nose of the plane and radar locked on the target until a kill was scored. Modern fighters have far more advanced missiles, radars and HUDs (the software in the cockpit), they quickly get a lock, fire off a missile, and immediately disengage. The F-14 could have been upgraded to include this ability, but it would have been costly and on an air-frame that was out of production.
Also, the avionics aspect is the most unrealistic part of these trailers. American pilots wear helmets that make them look like aliens, you cannot see their faces because their visual is like what Iron Man sees in the marvel movies, computer read outs in every direction they look. But... it's a movie, and they want to show off that they paid a lot of money to show you that they actually got Tom Cruise to sit in the back seat of an F-18, so I can forgive them.
This all ignores stealth. The F-22 and F-35 are the only mass produced stealth fighters in the world. Both go slower than Vietnam era fighters, but both have far more advanced avionics, are virtually undetectable by radar and are highly maneuverable. But, Top-Gun is a movie about the Navy, and the F-22 is not used by the Navy and the F-35 has only recently been introduced.
