"Then there’s the FM-X engine, Yamaha’s most sophisticated implementation of FM synthesis to date"

Debatable. There's SY77/99 AFM with multiple operator feedback and multiple waveforms.

"If you remember the once-misunderstood but now coveted FS1R synth, it’s like that on steroids."

Debatable.

Debatable. There's SY77/99 AFM with multiple operator feedback and multiple waveforms.

Ok, while AFM did have some very useful interaction via the routing of multiple feedback loops, the variety in source waveforms is simply accomplished in a different manner in FM-X. You are given Spectral Forms with both broad and narrow band waves that include "all" harmonics, just "odd" harmonics, and "resonant" peak waves. By adjusting the Skirt parameter you can create the exact same result as an operator fed back on itself. So let that debate begin. It may be a bit different from the way it was implemented in the old AFM engine. This and the additional two Operators will make this, as the two quotes you've pulled out of the article, pretty much an on-point assessment!

As we get deeper into the Montage era, look for articles/tutorials here on YamahaSynth, that will include both basic and advanced FM programming. We hope to even bring back some original programmers for tips and tricks...

One touch of the Montage and its FM-X engine will surely convince you that this is unlike any you've encounter previously.