Cubes is always going to see things through his rose colored glasses when it comes to his players.
I live in the Metroplex, and there is no doubt DN is an awesome talent and a great player - the Mavies would be a .500 club at best without him IMO. He is one of the top ten current NBA players - BUT.......
There is no way on god's green earth he could displace a top ten or even top 20 player All Time player without more playoff success than he's had to this point. Sorry. A first round exit three out of the last four years is not what a top ten all-time player does. He is also a below average defender.
I don't think you could even put him ahead of guys like Karl Malone, John Stockton, Julius Erving, Moses Malone and a bunch of other guys of that ilk. Those guys keyed multiple championship appearances and even an NBA le (1983 for Erving and Malone).
He's a terrific player, but Cuban can't help himself when he talks about his guys. He overvalues and overpays his own guys too often (in part because he can). I will say Dirk is a top dollar talent because he does perform at a very high level (in the regular season especially).