They did in vanilla too. Its always been WoWs way. You master one raid then move on up to the next. Hell even vanilla had 4 Or 5 raids. The only difference is that WoW intends for an xpac to last 2 years rather than 6 month Dlc and they actually have the content to stretch it out. I think Destiny is off to a rough start but so was WoW in its day. Give it some time and it'll either get better or fade away. Hopefully it'll get better.