We do not provide IP ranges for whitelisting. Part of the reasoning is as you described, in that the IPs can change at any time. Just because you might be diligent and able to update the whitelist on in a timely manner, it doesn’t mean a lot of other apps can or will which can lead to disruptions for merchants.
I probably can’t give the entire reasoning too much justice, but that is at least part of it.
Cheers.