I think, that these sort of discussions tend to coalesce around goal-scorers, and, inevitably, people playing in the last 40 or 50 years or so.
Agreed, but it's very hard to judge a defender when his performance is based on things not happening. Much of their work goes unseen and is "positional".
A Goal Keeper stands a better chance because it's clearer when they prevent a goal by their actions.
However, it's always going to be a forward or goal-scoring midfielder I think.
The game is ultimately about scoring goals and scoring a goal in the modern game is extremely hard to do, hence the hefty price tag on players who can do it regularly.
I think what unites people around Lionel Messi is that he seems to play for the joy of the game. As mentioned above, he seems to ride challenges (some of them designed to scythe him down) rather than fall over, even when he would be perfectly entitled to do so.
By the way, he just scored another Hat trick to become the highest goal-scorer in Champions League history...to obtain one of the few remaining records he doesn't already own.
Here's 5 minutes of magic. Really, if you don't like this then you will never like football. Most players would be dining out for life on just one of these.
Check out the final one, it out Maradonnas Maradonna.
https://www.youtube.com/watch?v=603JM1adqRA