One important difference, for Apple, between IBM and Motorola is their internal use of the CPUs.
For IBMs 970 to be useful to IBM they have to be competetive with Intels Xeon (at least for the blade servers, IBM might also have other plans for the 970 outside computer CPUs)
For Motorola the G4 is a good processor in embedded applications and they have no interest in the G4 as a computer CPU.
With such divergent goals for the G4 it is not stange if there has been a lot of armtwisting between Apple and Motorola, and that is allways a bad situation.
Regarding the PPC scaling. When the 9600/350 came out the Peniums were at 266 or 300 MHz IIRC. Then the G3 came that dropped a bit in clock speed but gained in performance
So from the first PPC in 1994 to the G3/450 in the spring of 1999 the PPC was on par or a bit ahead of the Pentiums.
Then we had the G4 clock down, the AMD 1 Ghz Athlon starting a real race between Intel and AMD in January 2000, while the G4 would be stuck at 500 Mhz until 2001
So 1994-1999 the race was made by 601 and then the 604 and lastly the G3. All 3 CPUs made well and it was a good period only marred by the nonnative OS and applications during the nubus PPC year. 1999-2003 have not had 3 diffrent CPU generations but only one the G4 and the kindest I can say is: at least it has been consistent
the 2x clock speed gap it lost in 1999 and 2000, it has keept 2001 and 2002 and 2003 without any signs of failing. If anything it seems to err on the safe side and sometimes archiving almost a 3X clock gap