Actually from Zen 4 to Zen 5 there is a little more than one year and a half (supposing that they will indeed go on sale in July), almost matching the AMD announcement done around the launch of Zen 4 that they will shorten the time between generations from 2 years to 1 1/2 years.
Of course it's real. But not only is M4 significantly faster in ST, it'll probably 3-4x more efficient than Zen5 mobile just like how M3 is against Zen4 mobile.
This difference in efficiency cannot be explained by node advantage alone as N3E vs N4 is probably around only 15-20% more efficient.
I wonder how much of the performance delta there is the OS. The performance benchmarks for Zen won't be running on OSX, credible risk they're running through the overhead of Windows.
