It simply isn't true. How could I get through Echoes without having to go rant about it, while I have to do so now?
Let's see...
-You have to beat mini-bosses and bosses to progress through the games
-You also need to search for items and upgrades that will help you solve puzzles
-Both have free roaming to almost any extent
-Heart Containers and Energy Tanks. Nuff said.
-Neither of the main characters really say anything
-Dark World and Dark Aether?
-To go with the above, Dark Link and Dark Samus
Really, the only differences are the amount of NPCs in the game, the way the game is controlled, and of course the difficulty. If we were talking only about the storyline or music, there wouldn't be as much in common.