All I'm saying is that preemptive multitasking isn't impressive from the computer hardware's point of view, because just about anything can do it properly 
That last word invalidates your statement.
Properly would mean efficiently and with a measure of utility and many early microprocessor can not provide that.
The 6809, yes. The 68K, yes. Early Intel processors? Not well at all.
Minix was probably the only example of this that worked reasonably well (until the '386).
