Aww come on. Just because his cars didn't have a shot at WDC those years doesn't mean they were slow. In 2002 McLaren was new to Michelin. In 2004 they had some problems with the famous MP4/19. They still won at least one race those years. In 2006 they weren't very good, but hadn't Räikkönen crashed it in Hungary it could have been a winning car too. In 2007 and 2008 nobody seriously expected a winning car considering the competition. Still in Fuji 07 it was very close to victory only to be ruined by Vettel. And in 08 the car won in Monza...
By the way, the MP4/21 is considered a Newey-design, but he wasn't with the team anymore when the season was on.
I believe most other designers would be happy about such a record in their CVs.
Now we are talking semantics. No F1 car is slow, as they all could run rings around any supercar you can find on the street. Regardless, compared to the top contenders of those years, overall the cars of the aforementioned years were slow by F1 standards.
MP4-19 didn't win any races, that was the MP4-19B which was a totally revised new version. MP4-19 was slow.