Muhammad Ali – reactions i really don’t understand

Muhammad Ali, unfortunately in my view, sadly and I think tragically, died yesterday. There are many reactions to the event which I do not understand let alone comprehend.
Here’s a list:

“Muhammad Ali was the greatest“: Sure, he was a very interesting character. He was a boxing champ, a cultural icon and a social role model for some people – which i respect – and a human being. However, what do people refer to when they say “greatest“? Is it a reference to him calling himself “greatest” as part of promoting his bouts? Is it “greatest” boxer? Is it “greatest” in terms of some other element combination?
Indeed, am surprised people think “greatest” is kind of cool.
If we have “greatest”, then we have slightly less so, and so on – we get to cultivate a hierarchy, or even worst – having hierarchies in general.
Now, isn’t it that precisely the kind of thinking that imagines hierarchies to be natural and needed, normal and unquestioned – is the kind of thinking and culture that allowed slavery to thrive? Is it not that hierarchical culture allows accepting rather than correcting the effects of slavery on communities and indeed its mutations into using wage and debt to own and control people?
Links?
http://www.latinamericanstudies.org/slavery/SF-2003.pdf
https://books.google.co.uk/books?hl=en&lr=&id=IyodFB4SdOIC&oi=fnd&pg=PP2&dq=hierarchy+and+slavery&ots=fVs0ELVH6_&sig=_lhTN9djWHv_qB4GBJh1KsmI-Tw#v=onepage&q=hierarchy%20and%20slavery&f=false
http://personal.tcu.edu/swoodworth/Sparks.html
https://prezi.com/zg2vszp5fgfo/slavery-abolition/
https://www.mpg.de/10421772/human-sacrifices-hierarchical-culture
http://www.du.edu/korbel/hrhw/researchdigest/slavery/india.pdf
Maybe not entirely linked.
I might be over stretching the links here, however I think the point is valid in the sense that in relation to a person that rebelled against slavery ramifications – current links, perceived or imminently ontologically integrated in our social fabric – it might be ok to ask – greatest? How, why and WTF??

(* btw – a friend pointed out that they heard an 80’s bbc interview with Ali saying he used the “Greatest” thing as way to promote..)

Muhammad Ali was a boxer, a sport. (I have reservations about that activity as a sport, but that’s not for now and here..) As a sports person, he crossed into cultural, social and political spheres.
Is it not curious that he is hailed for transcending the sport – while culturally and socially we find it acceptable to suppress – if not outright oppress and ostracize – sports personalities who happen to voice social, cultural and critical views?
Sure, Muhammad Ali was subjected to such a treatment too – however it seems curious that companies like NBA who marginalise people who voice critical views, hails Muhammad Ali for being critical of power. No?
http://www.edgeofsports.com/