That might be slightly mispresenting the point. While it is true that before RF all raids and ex primals were in the DF, it was not possible to queue into the latest raid or ex primals without full party. It was technical limitation, not just practical one. You were forced to gather one, either by having a static or, indeed, through PF. However both of these methods were limited within the server drastically cutting the pool of possible participants. Raid finder was an attempt to give change to break this server barrier for the content that was, rightfully, considered too hard to be released to totally random parties. Howevr while announcing "practise from start" or "after adds" or similar worked to a point in PF those different options in RF didn't achieve the same result, they only divided the pool of non completers into different queues that never got through. This the only usable part of the RF was the ultimate toggle for completion.
Cross server PF is the second take to the same situation. Does it force people to be a bit social to actually look for a farm party? Yes it does. But that's not different from the same limitations in place before RF.