I've been using Swiftkey for years now, having tried many many alternatives and finding it far superior than other options.
The only thing that is missing is the option to customize a key. For example, replace a symbol with another.
I have almost no use for the comma(,) and I use the question mark(?) all the time and the question mark needs two presses which is annoying, and really slows typing.
I am guessing Swiftkey has statistics of people's keypresses, they can check frequency. My guess is most people use the question mark a lot more than the comma, so why not make it default instead of the comma (if not adding the customize feature).
Many thanks for the best keyboard.