Difficult or easy for WHO? One person's cinch is the next person's struggle. A person's overall intelligence can be approximated with IQ tests, which show that the average person, even in the USA, is not very smart. The pre-med pool is still a diverse group.
The (intelligent yet) uninformed: There are people who have known that GPA + MCAT = Medical School since their high school years, and planned accordingly, and people who had no clue that either mattered much.
The (intelligent yet) underserved or distracted: There are people who were able to focus almost solely on GPA, MCAT, and other pre-reqs. There are other premeds who got stuck dealing with extenuating circumstances.
The (intelligent or less intelligent) person with a social mission: The person who isn't a premed because s/he thinks s/he's smart, but because s/he has noticed something in society and medicine that makes him/her think s/he has something special to offer future patients. This includes but isn't limited to people who want to serve the poor, a minority group, a disadvantaged area, change the healthcare system, and/or know they will try harder than most other people (perhaps anyone else) at something important to them. This medical school candidate might speak a lesser known language or be familiar with areas of the world or a member of a subculture or minority group that's truly in need - and that most people don't understand well enough to help.
The really smart dumb people: These are the people who are extremely gifted in some areas, and almost equally lacking in other areas. Some people are extremely good with language skills and people and just lacking in math and science; or just the opposite.
Perceptions: Those who believe that they are smarter or dumber than they really are - which might be just about everyone, except when it's to an extreme. When noting that perceptions =/= reality, professional IQ tests become necessary in answering this kind of question by OP.
Those who need a challenge: I'm sure there are some people on here who are very intelligent AND have everything they need to maximize their achievements. In my experience, super smart people are often in need of a challenge and are sometimes tired of less intelligent people being catered to.
Conclusion: If you know what you are doing and have superior intelligence, and don't encounter other obstacles, getting into medical school is probably "easy" for you. However, I personally believe that a certain number of those who don't find it "easy" are also needed in medicine.