There are many covers that have their own credentials.<br />
Joe cocker: 'A little help from my' friends; far better than the Original. 'If not for you'. Olivia Newton John, as good as the Dylan version. 'Mother' Barbra Streisand, a different take to John lennons but awesome, 'Jealous guy, Bryan Ferry, again not better but as good as the original.<br />
Many many more.<br />
If no one covered others music, where would we be with Beethoven, Mozart, Haydn etc etc, no recordings of the originals there.
You are absolutely right that it takes a lot more creativity and originality to create a good song than to make a good cover of an existing song. But yeah some covers are in my opinion a lot better than the originals. You have to keep things separated here - I can appreciate a cover more musically wise as it appeals to me but that doesn't mean I don't give credit to the original or appreciate that too.
Sometimes a cover is better than the original and there is also the fact that many of the songs people think are originals are in fact covers themselves of even older songs.
In most cases the original is better. Example Live and Let Die, paul mccartneys original than the guns n roses by a mile! And then on the other hand, you have jimi Hendrix All the watchtower, which is better than the original by bob Dylan! :)