...the constant slow down to speed up...
I've got no qualms with reducing to get the required spacing from the bloke in front of me who is doing 330 knots and then putting the pedal down to maintain a high speed sequence. As long as I know to expect this so I can adjust the profile accordingly I'd say it's actually an efficient use of the airspace.
PERs problems are more about airspace and where all the aircraft are going to/from than it is about the ATCOs themselves.