That's almost 1 extra over of someone else bowling too:This is basic cricket logic and it is weird that it is being debated against.
Anyone who watched McGrath in his career can attest to the pressure he created just by building up to a wicket and keeping things in control.
For some reason, CW seems to fetishize low SR bowlers like Steyn, etc. but the reality is that he was the most hittable and loose of any ATG.
I tend to think what is the situation when the bowlers is not taking wickets and in the case of a low ER bowler, the situation is still under control. It doesn't matter as much if he takes an extra over to get a wicket.
Also as mentioned, low SR bowlers like Waqar, Rabada and Steyn tend to bowl less overs per test for whatever reason.
-Someone worse bowling
-Other bowlers getting tired
-The ball condition typically getting worse for bowling
-Bowlers having to bowl at a set and higher quality bat.
OFC 1 extra over per wicket isn't giving a big advantage. But that's a function of comparing 2 bowlers with very similar SRs. If you have a bowler that takes one for twenty every over, you have an ATG bowling lineup even if the rest of your bowlers are poor. A bowler taking 1/20 every 10 overs is only pulling a poor attack up to the level of decent.