Get Sony RX1R II at B&H Photo. Strongly recommended: optional Sony LHP-1 lens hood (56% off today!) to protect the front of the lens (and as a secondary consideration, stray light) as well as at least three Sony NP-BX1 batteries.
Flare is evaluated from f/2 through f/22 with one series, and two other examples are presented.
Flare behavior changes with aperture, so this is a very useful series to examine.
A lens can have weaknesses of various kinds (some of which can be pluses at times), but when flare degrades images in dramatic lighting, there are no options for dealing with it other than not making the shot, or using some other lens or camera. But what if a camera has a fixed lens, the only one? That gives me pause, because I am a particular fan of dramatic lighting.