IMO you need both. Trams for local transit, metros for faster mid-range transit, and finally urban rail for long(ish) range transit.
0) trams are hardly unreliable
1) tram lines are routinely changed around
2) in Switzerland, there is no distinction between local and remote public transport. This has the advantage that you can use the regular trains for short hops. Zürich itself has 20+ railway stations.
Zürich has really opened my eyes for what a good tram network can do.