I often hear, "You should only pick your wedding photographer if they use a particular brand of camera/lens." (Usually Nikon or Canon.)
In March 2014, I was introduced to the Micro four thirds mirrorless system,in the form of an Olympus OM-D-EM1 which at the time, according to Olympus was designed to outperform the DSLRcamera (Digtal Single Lens Reflex cameras.) This system is smaller and lighter than my Canon kit but with equally good image quality especially when using professional lenses from the likes of Olympus, Panasonic and Sigma, particularly those with a wide aperture/fixed focal length.
I dipped my toe into the micro four thirds system but kept my Canon kit at the same time. However, in November 2016, I finally took the plunge and now exclusively use that system. For weddings, I use two cameras, an Olympus OM-D-EM1 MkII with an Olympus 12-100mm Pro lens with a constant aperture which is better in low light and can be used for creating "bokeh" which is where the background is out of focus and the main subject is sharp and in focus. I have another lens for use with the Olympus, a Sigma 19mm Art Series lens (with the empasis on "Art") with a fast aperture again for making the subject pop out of the background.
These lenses have a 35mm (think of film days) equivalent of 24-200mm and 38mm respectively. So if I'm stuck at the back of the church or other venue as I have in the past, I can still capture those important shots such as exchanging the rings and the first kiss. The 12-100 lens is the perfect wedding lens as I can shoot from wide angle, to full length portraits through to head and shoulder shots and exchanging the rings without getting "in yer face!" The 19mm is also a lovely portrait lens.
I also have a Panasonic Lumix G80 with a Lumix 25mm lens, again with a fast aperture and a 35mm equivalent of 50mm. The camera body, like the Olympus is weather sealed. I have a Lumix 100-300mm lens for this camera as well so potentially, I could stand across the road in the car park and still get a shot of you exchanging the first kiss in the church or other venue as the 35mm focal length is equivalent to 200-600mm!
With the EM1 MKII or the G80 and the 12-100mm lens combination, I can always carry on shooting if you're having a winter wedding and it's freezing outside as they're both weather sealed - the Olympus body and 12-100 lens are also freeze proof down to -10! Your friend or friend of a friend with the cheap camera/lens will be running for cover by this stage.
So if my images have a "blurry background" this is done entirely for artistic reasons such as the image of the bride and flower shot and the groom in the mirror. The same goes if I cut heads off, this is done on purpose to emphasise a particular detail such as the bouquet shot below.
I offer the services of a second photographer as an extra backup and to cover your wedding from different perspectives, something your friend or friend of a friend wouldn't even consider.