Tupac is a legend and ranked close to the top because of the impact his music had. Quite a few people underrate his flow and actual ability which I've always found crazy. He made you feel what he was saying as much as probably anybody that I've personally ever listened to in music as a whole. Not everything had to be wrapped in riddles and insane word play like seems to be the case nowadays, that's not what makes a great lyricist, it's about a lot of people being able to relate, understand or feel what's actually being said and Tupac did that probably as well as anybody has done in rap music. Music alone he put out classics, when you then combine that with the effect his music had on people and the rap game itself and how much effect he eventually had as a person too you easily get one of the most influential and important people to ever be a part of rap or even music itself for that matter. There's different levels to the game, there's not many bigger than him. And as a rapper alone he had genuine classics that stand the test of time after 25+ years, no way is his music outdated, a lot of his music still easily fits in today without sounding out of place at all.
Big fan of Kendrick and I rate him highly but the 'easily top 5 ever' and disrespect for past legends like Tupac, Biggie, Nas and not even mentioning people like Cube, Rakim etc as if it's a foregone conclusion is a bit crazy. Obviously it comes down to personal taste in a way as well so I've got no problem with anybody thinking Kendrick is top 5.