The title of these movies is...without doubt "The Lion King". So who do you think the creators wanted us to believe was "The Lion King". Is it Mufasa? Simba? Are they just referring to the title "Lion King"?
Personally I think they're referring to Simba when they title the movie "The Lion King". He's the main character and the movie follows him through cubhood and into adulthood.
But what do you think?