It was actually 9 in a row. Never lost before the semis there in the 12 years he played. Also holds the record for most consecutive matches won indoors at 66.
Lendl has lots of amazing "consecutive" records. He holds the record for the most consecutive finals at the WTF (9), the US Open (8) and the shares the record at Roland Garros (4) and the Australian Open (3). That's 4/5 of the biggest tournaments in the world.
5 years in a row with a +90% win-percentange is also another record no one else has been able to beat. 19 slam finals speaks for itself.
You can't ignore the effect of surface homogenisation. Lendl made 7 Wimbledon semi-finals playing on fast grass. That's equal to Federer and only 1 behind Sampras. What would he have done on todays grass?
But of course his records don't come anywhere near Nadal's
No, those records aren't good enough on non-homogenised surfaces.