The Frenchman enters the season-ending Abu Dhabi Grand Prix having secured all 29 points amassed by the US team in its maiden Formula One campaign.
Although his team-mate Esteban Gutierrez finished just outside the points-paying positions in 11th five times this year, the Mexican was not retained by Haas for 2017.
Asked to rate Gutierrez by reporters at Yas Marina Circuit, Grosjean said: “I can tell you that Esteban is very fast in qualifying, he’s got good pace over one lap clearly, he is much faster than what people are thinking.
“In the race, he’s been a bit struggling this year. He did not do any race last year [Gutierrez served as Ferrari test driver in 2015].
“But for the team you need the two cars to score points. Not in an equal manner as someone may have a bit of luck one day and have a really good result, but you need for the constructors' championship to be able to score more points with the two cars.”
When pointed to him that Gutierrez has suffered his fair share of reliability issues on his return to F1, Grosjean believes setbacks even out over the course of the season.
“Over 21 races, there are always some races where you'll be unlucky and some where you'll get lucky. It balances itself.”
Grosjean is set to partner Kevin Magnussen in 2017, after the latter signed a multi-year deal with the American outfit. His future team-mate believes the Dane has what it takes to help move Haas forward.
“He's shown that he's a racer, in Singapore and in Russia holding a position with a car that did not have the pace to be there. He managed to keep the position.
“That's what the team wants. He's a great driver so I'm looking forward to [working with him].”
Haas is currently eighth in the Constructors' championship, 34 points behind seventh-placed Toro Rosso.