That is a gross oversimplification. Receiving a dose of 200uSv via exposure to something like x-rays is very different to being exposed to 200uSv that includes particulate matter that will accumulate inside the body. The former is a one time "hit", the latter is much more likely to lead to cancer because the material can sit inside the body slowly damaging DNA.
If you believe in the linear no-threshold model then it makes no difference whether the dose is received in a single hit or an extended time period.
Those who doubt LNT usually suspect a dose-response curve that goes in the opposite direction to what you are suggesting.
Particulate exposure could conceivably be worse for you due to the exposure being localised to one part of the body, but that has nothing to do with the timescale over which the dose is spread.
Sadly that XKCD chart and nonsense like the "banana equivalent dose" have spread a lot of misinformation about this.
The main issue with the concept of a "banana equivalent dose" is homeostasis of potassium levels, which again has nothing to do with any of the points above.