The idea was they would use the 769's so they could PRM the 150's. However they took so long to get into service they had to get the 153's in to fill the gaps. Whether the 197's will come into service quick enough to release 150 and 153's to reduce reliance on them remains to be seen.
It all depends on train crew training now. Hopefully there will be a few in service by the height of summer, maybe even one or two by May timetable change.
The issue arises when you don't have all train crew at certain depots passed out, so even if say the 197's are kept on Chester - Liverpool, you're still going to need a backup unit to cover if train crew don't sign the traction. When you start to branch out the units on further routes, with other train crew depots involved, then it becomes even more complicated.
So even starting to see them on Chester - Liverpools won't necessarily free up any units.
Start putting them on North Wales Coast services and you have 3 train crew depots involved (Holyhead, Llandudno Junction & Chester) all at different levels of training, where you could have 2-3 set of train crew working a service (Manchester - Holyhead for example). Chester train crew could work 197's from Manchester - Chester, Llandudno Junc. train crew Chester - Llandudno Junc and Holyhead train crew working over to Holyhead.
It would make sense to be cautious and confine them to Chester - Liverpool and maybe even Blaenau Branch for some time until a high proportion of train crew are signed off where it can be swapped to an old unit if necessary.