The reason why Roger couldn't do what Luffy will do, is because Roger was sick and he was born in the wrong timeline. So no, Luffy is indeed destined to succeed...
The plot at beginn was Luffy becoming the pirate king. The symbols back then were all given, the strawhat, everyone mentioning luffy behaves and says the same as roger etc. pp.. Absolute symbolism here. So Luffy was able to succeed back then what Roger already succeeded.
The plot just changed. Now the goal isnt Roger anymore, its joyboy. But the symbolism is exactly the same.