You can tell a lot by what cameras and lenses the DOP of a documentary chooses. You see, a documentary shooter has nearly a wholly different set of gear requirements than a narrative shooter, usually. Yes, some crossover between the two worlds does happen. Yet, light-weight and easy and fast while providing a good image tend to drive documentary camera selection. Consider most documentary shooters are carrying and shooting with small crews, and a camera choice and its ease of use become essential.
This post’s figures are based on the sampling from the feature-length competitive non-fiction films at Sundance, with 18 filmmakers answering a questionnaire. How did I get these numbers? I just took the information from the 18 filmmakers and put it all in a couple of charts via google sheets. 
39%! Of the 18 Sundance Film Festival documentaries, 39% used Canon cameras, and over 50% used Canon lenses. What is surprising to see is how many Canon lenses DOPs used to shoot Sundance Film Festival documentaries. Well, maybe not too surprising for some to see Canon used this way, the Canon C300 Mark II and now C300 Mark III are a dream to use as a documentary camera. A few documentaries used more than one type of camera and more than one type or brand of lens. 
The list below shows the cameras and lenses used to shoot 18 films from the U.S. Documentary Competition, World Documentary Competition, and Premieres. The data is based on the IndieWire cinematography survey.
Ailey. DP: Naiti Gámez.
- Cameras: Canon C300 MarkII, Canon C300 MarkIII,
- Lenses: Canon CN-E Cine primes; CN-E30-105mm zoom & L-series lenses
All Light, Everywhere. DP: Corey Hughes.
- Cameras: Sony FS7, Sony FS5,
- Lenses: Canon 30-300mm, Fujinon Cabrio 20-120mm, Zeiss CP.2 (15mm & 35mm), Canon 24-70mm, Leica Summicron 50mm
At the Ready. DP: Maisie Crow.
- Cameras: C300 MarkII, Canon 5D Mark IV, Panasonic EVA1,
- Lenses: Canon Zoom Lens CN-E 18-80mm, Canon Zoom Lens 24-70mm f/2.8, Canon Zoom Lens EF 70-300mm f/4-5.6L IS
Captains of Zaatari. DP: Mahmoud Bashir.
- Cameras: Sony a7S Mark iii, RED Dragon
- Lenses: Master prime
Cusp. DP: Isabel Bethencourt and Parker Hill.
- Cameras: Canon C300 Mark II
- Lenses: Zeiss Standard Speeds
Homeroom. DP: Sean Havey.
- Cameras: Sony F5, Sony a7S
- Lenses: Canon 24-70mm f2.8 and 70-200mm f2.8; Sigma 50mm T1.5
Misha and the Wolves. DP: Will Pugh.
- Cameras: ARRI ALEXA Mini
- Lenses: Angenieux Optimo T2.6 15-40mm, Angenieux Optimo T2.8 45-120mm
My Name Is Pauli Murray. DP: Claudia Raschke.
- Cameras: Canon C300 Mark II
- Lenses: Canon Cinema Primes, 17-120mm Canon Cine Zoom, 18-80mm Canon Compact cine zoom
Philly D.A. DP: Yoni Brook.
- Cameras: Canon C300 Mark II, RED Gemini
- Lenses: Canon 24-70, 150-600
Playing with Sharks. DP: Ron Taylor, Judd Overton, Nathan Barlow, Michael Latham, Jono Heighes.
- Cameras: ARRI ALEXA Mini, Sony F55
- Lenses: XEEN Cine Prime Lenses
President. DP: Henrik Bohn Ipsen.
- Cameras: Sony FS7 Mark II
- Lenses: Two zoom lenses – a Canon EF 24-105 mm and an old canon 28-300
Rebel Hearts. DP: Pedro Kos.
- Cameras: Canon C300 Mark II
- Lenses: Canon L Series, 35mm prime and 70-200
Sabaya. DP: Hogir Hirori.
- Cameras: Canon C300 Mark II
- Lenses: Canon 24-70 f/2.8
Searchers. DP: Daniel Claridge and Martin DiCicco.
- Cameras: Canon C300 Mark II
- Lenses: Zeiss 28-80mm & 70-200mm Compact Zooms
The Sparks Brothers. DP: Jake Polonsky.
- Cameras: RED Monstro Monochrome
- Lenses: Panavision Primo Artiste
Street Gang: How We Got to Sesame Street. DP: Luke Geissbühler.
- Cameras: RED Weapon
- Lenses: Canon CNE Speed Primes
Users. DP: Bennett Cerf.
- Cameras: RED Gemini, Blackmagic Pocket 6K
- Lenses: Master Primes (18mm, 35mm, 100mm Macro)
Writing with Fire. DP: Sushmit Ghosh & Karan Thapliyal.
- Cameras: Canon 5D Mark III
- Lenses: Canon 24-70, 50 (1.4) and 28 (1.8)