The games are not in progression, it's more like version number.
When each version was the live version they were just called Runescape. RS1 (now called Runescape Classic) is more of a 2D game, it later got upgraded graphically to 3D and became known as RS2 to distinguish it from the old version. Then a new combat system was introduced so it became what people now call RS3 but is actually just the current version of Runescape.
RS3 has all the content the previous versions had, with perhaps some improvements to the older content and obviously more updates since it's the current Runescape. Same as RS2 had all the content RSC and it more updates since it was the Runescape, when it was live .
05-Aug-2017 09:32:32