I've always been genuinely curious about this. Is this more about superiority of equipment, training, tactics or all of the above?

All of the above. US/NATO forces use effectively "combined arms" techniques. The first gulf war is an excellent example of this. First was intelligence gathering, mapping out SAM/AA and radar sites as well as their characteristics (frequencies, etc.) Early on a series of drones were launched to get the SAM radars to light them up, making it possible to locate and characterize each radar site. Then the first wave of attacks concentrated on taking out the ground based SAM infrastructure using conventional bombing attacks (say, tomahawk cruise missiles hitting the known locations) as well as radar-homing "anti-radiation" missiles (ARM). Additionally, because the radar signals characteristics had been determined that made electronic warfare and radar countermeasures that much more effective. Aircraft like the EA-6B Prowler and the F-111 would be able to send out specially crafted radar signals of the exact frequency and characteristics used by radar sites to spoof different radar returns, making the radar effectively unusable.

Meanwhile, command and control systems were being hit including communication lines and upper echelon meeting places. The F-117, for example, was hitting high level targets in downtown Baghdad in the earliest moments of the gulf war. And then airfields were being hit, taking out runways and destroying planes on the ground.

When the airplanes took to the sky they flew air superiority wings protecting bombing wings, and the battlespace is monitored by AWACS radar planes. So you have a high number of planes that are working in a coordinated manner and making use of tons of data from radar facilities and so forth vs isolated, unsupported groups of planes that have numerical inferiority.

That alone would be a huge advantage even if the technology and the training were identical, but when you add in the edge that superior technology and training provide it becomes overwhelming.

Also, most people know of the "Topgun" school, but most do not know the details. There were tremendous changes in the nature of aerial combat in the 1950s and 1960s as planes transitioned to jets and became capable of supersonic flight, onboard radar systems got added, radios became better, and a whole host of guided missiles became primary weapons systems. Air to air guided missiles have many limitations and need to be fired only under certain relative conditions of trajectory and airspeed between the attacker and target, and it's not always intuitive how to transition from a given relative configuration to one where firing a missile will have the highest chance of hitting the target. Additionally, maintaining an upper hand in air to air combat is tricky and requires a special set of skills.

In the 1960s there were two seminal works that laid the ground work for training pilots in the future. One was the Ault report, which was a very brutal look at the performance of American pilots in Vietnam up to that point. It's not to say that those pilots were doing poorly, only that they were making lots of mistakes that could be avoided with better training, especially in terms of knowing how and when to fire their weapons to have the greatest chances of a hit. The other was the combined work of Col. John Boyd and Thomas Christie in formulating foundational theory of modern fighter jet combat. They came up with the idea of the OODA loop (Observe, Orient, Decide, Act) and "Energy-Maneuverability theory". The basic idea of OODA loop theory is that a pilot should be cycling through the Observe-Orient-Decide-Act phases as quickly as possible (without compromising the quality of each phase), and in so doing will maintain an edge in encounters. This is because the whole system, not just the pilot, is like an organism, and the OODA cycle time is characteristic of the reaction time of the organism. Having a faster reaction time is advantageous and can make it possible to steal the initiative from an opponent or to dull the advantage of the opponent having the initiative. This applies regardless of the maneuverability of the plane a pilot is flying, though more maneuverable planes tend to encourage a faster innate OODA-loop. EM theory forms the theoretical framework around which a pilot maneuvers their plane to avoid being at a disadvantage to the enemy while working toward gaining an advantage and to coming into a configuration where releasing weapons is most effective. That training has been the basis for fighter pilot performance in western countries since then, and it's resulted in extremely capable pilots.