The previous idea for this service was that it would go to Manchester all day, as it currently does at peak times. That would also provide 2tph all day at Eccles and Patricroft. Of course it's rather off the table now...
I would argue that it is in fact reasonably necessary. Either Whiston and Rainhill are worth serving or they're not. If they're worth serving they need at least half-hourly to be any use. If they're not worth serving, close them. The same applies with the Lea Green / St Helens Junction split. Of course, going to Wigan via Golborne would be notably more useful than going to Warrington Bank Quay is. Indeed this was hinted at by the fact that one service terminated at Earlestown and immediately ran back to Liverpool Lime Street empty to resume another working. Not least because it would offer regular Newton-le-Willows to Wigan service.
Does this change also reduce St Helens Junction and Rainhill to 1tph, and Earlestown to Liverpool? Also all stations except St Helens between Huyton and Wigan now 'permanently' 1tph. Not great for a suburban stopping service.
With Preston-Manchester Victoria down to two-hourly as well it seems like the cuts are focused on the lines which just had a fortune spent on electrification a few years ago? If the TPE frequency over Chat Moss doesn't come back is there much need for the four tracking around Huyton either?