Most retro game fans express the greatest achievement of true parallax to be horizontally sliding strips. Many say that the PC Engine is only faking it, but it's still so impressive when several strips move at once. So much parallax in Genesis/SNES games is done in "software" that there's likely more with it than without.
Dual tile layers are used in many ways, intended for many different things and are not simply a "hardware parallax" feature. What they are often used for is faking large sprites for things like bosses, when the PC Engine usually uses real actual sprites. Are those fake sprites? Is that hardware support for sprites? Can tiles be sprites, even though it's being insisted that the opposite doesn't count?
The Genesis' combination of features and how everything functions, just happens to make it the easiest console of the generation to do realtine rendering. Which is why most polygonal games were on Genesis and why it's so good at scaling and rotation. If it's not exploiting a single feature meant for general use, does that mean it's not hardware support and instead is "faking" it?
The PC Engine has unique hardware features which make it better at animating fast and cycling colors, which allows all kinds of parallax and transparency effects. If consoles like these are so good at rendering effects without dedicated chips and if the effect is identical or superior to what some dedicated chips can do, how is it "fake"?
If concentrating on making the hardware fast enough to do these effects and more, along with support for giant sprites, was all because of the hardware developer's intention for them to be used for parallax.. does that make it real?
Using multiple hardware tile layers for parallax is no different than using multiple hardware sprites for parallax or a single hardware tile layer for parallax or a combination of hardware tiles and sprites for parallax. In all cases, parallax is not the dedicated function of the hardware features used and all features used are hardware supported.
The most obvious example of how ridiculous the myth of "multiple-tile-layers = hardware-parallax" is the Neo Geo, which has *ZERO* tile layers. This is most definitely *LESS* hardware support for parallax than the PC Engine, which can do all kinds of parallax using a tile later, as well as flex its sprite power for parallax, just like the Neo Geo does.
Does this make even parallax-free scenes of Neo Geo games "all fake"?