There is no definitive way to answer your question. It depends entirely on your target audience and how much effort your company is willing to put towards support a, I will admit, likely minority. Some of us need to.
To what extent are those platforms unable to support a better browser? For instance, Firefox works all the way back to Android 5.0.
Browsers on devices (sometimes iPads, sometimes Android) that are inside touch-screen kiosks.
Some of the ones I work with are in places so remote, it would take me three or four days to reach them if a software update goes wrong. Then another three or four days to get back to the office.