There's definitely not "one" central server. Depending on how they route your connection (do they proxy you or redirect you), you might still just be connected to the server you're playing on, but the "ping" is also more complicated in itself since the protocol is more complicated. Instead of information from the client to the server which updates all the dynamic entity states, you are instead sending input commands and getting video and audio back. So, not only would "ping" measure something entirely different, it would possibly be optimized for in the path between you and the remote differently as well.

They may have decided that instead of providing a metric that might lead people to believe it's similar to and implies the same thing as it did in the past, they'll remove it. If so, I would hope they would put something semi-equivalent in it's place. Maybe they did, but it's so removed it's hard to locate?