I think the reason people say DKC Returns is "easier" than the SNES is because it was cleverly designed to be more "forgiving" than the SNES titles.
In the SNES titles, both characters could only take one hit, meaning you had two lives. Then you had the balloons which were sparse and somewhat rare unless you knew how to scour the levels and collect those bananas and KONG letters.
The Wii game has the following features and enhancements:
- Both DK and Diddy have two hearts each, meaning that they can take two hits before they are defeated
- Not only are the balloons plentiful you can buy and horde them by visiting Cranky Kong's shop
- Diddy has a hover jump which makes platforming easier
- In the event that you can't beat a level there's the super guide feature that beats the level for you
With all those features in place, the game is indeed "easier" than the SNES games. However, the designers at Retro were clever as instead of dumbing down the levels in order to follow along the features that make the game easier the levels themselves got more challenging, meaning that there is a lot more stuff to avoid, more reflex based jumps, cleverly placed enemies and random events that throw you off.
If you compare the games you will see that a lot more things are happening on screen than on the SNES games, which contribute to the challenge of the title, and thus why I think its a hard game.