You question is quite ambiguous. Ragnarok is an MMO, and whilte Dota2 and LoL arent, they are still network-heavy regardless.
If you dont know much about networking, then you need not worry about this sort of network usage. But in short, probably not. The network module of SFML is sufficient for an intermediate level of networking. When you get into MMOs and network-heavy applications, you should look at engineering your own networking libraries.