I am not sure that anybody can make a categorical statement about which team was the greatest of all time. If you base the answer purely on the number of consecutive tests won - then that may be a coorect statement.
However, ptior to 1997-98 the record of 17 consecutive tests won was held by the All Blacks. That happened while th sport was an amteur sport - not in the professional era. So I assume that with his wording mozart referred to the period since professionalism was introduced after the 1995 WC.
Now lets analyze the situation further. Successive wins by a team over an 18 months period could be influenced by the situation pertaining to the strenth and weaknesses of the opposition - as well as whether the games were played at home or not. Lets start with the opposition team situation.
* In 1997-98 the All Blacks team was not as strong as the one they developed subsequently
* The Wallabies and POMS went through a slump - as they just started to build new teams to contest the 2000 WC.
Now lets look at the games issue. The run of wins did not include a WC and started off with a record win against the British Lions (35 - 12) ) and against the Wallabies (61 -22). After that the number of wins was more or less half ay home and half away..
Now lets look at the present All Black team with their 15 wins in a row. The started off with six wins in the WC - ie home games. They then beat the irish 3 times at home - followed by six games in the Championship - of which only three was away games. In th process they played 12 of the games in New Zealand and only three away games. However, the fact that they did win 15 games in succession - really shows a great team.
If the argument is about a virtually unchanged team playing over a period of 18 months winning 17 consecutive tests - and that is th only norm applicable - then the answer is yes they were the best team during the professional era - since they did manage to win at home and away.
However, if there are other norms applicable like performances of teams over a protacted period of time - then the All Blacks must be rated as having had since 1995 the BEST TEAMS n the world during the periods they were ranked as no 1 in the world.