Following an idea from here:
Here is a map displaying catchment circles and gaps in Merseyside's Merseyrail system. The catchment circles are of 600m and 1000m radius.
Note the close spacing of stations in Liverpool and Birkenhead city centres and large areas around Liverpool city centre which have no station. Is this where planners perceive the distance into town is too short to warrant a train journey? Note also the various agglomerations of closely located stations with overlapping catchments.
Merseyrail is a perplexing beast. Neither true metro, nor true suburban network, somewhere in between. In the centre it displays characteristics of any classical metro system, with frequent train spacings; further out it is a suburban/provincial commuter railway like any other. Its stock is electric, but of a regular type 508 found all over Britain's provincial and suburban railways.
Particularly, the neglect of inner city Liverpool in its catchment rather rules out its usefulness as a metro to a large extent. Particularly this bias toward the outer extremities means it might best be compared to the RER routes in France or the S-bahn systems in Germany and elsewhere.
What could make Merseyrail a true metro?
1. Lighter rolling stock. I don't mean lower capacity but a 'light rail' rolling stock, say like DLR, with faster acceleration and braking. would give a different image to the network and define it as separate.
2. More lines. There is potential to reopen sections of tunnel and surface line in Liverpool. Around the inner city this could provide a more metro-type service.
3. More stations. As the gaps map shows, there are plenty of spots that might benefit from a station.
4. Segregation. Various sections of Merseyrail currently use shared track and overlap with mainline services. The distinction needs to be made.
5. Autonomy. Complete autonomy of operation and ticketing, under the control of Merseyside Council.