Some months my data volume doesn't last till the end of the month. I use SMS instead of the Signal protocol then.
Yes I might be a minority, but if you're not the market leader, cutting out minority groups of users will not make you more successful.
What's your mission: Giving secure communication to everyone or become the next WhatsApp?
"Reduced" is a very kind characterization, even if it's literally true - in my experience (with Vodafone and Three) this means ~64kbps which makes even messaging apps functionally unusable.
Since I started traveling more, I use my eSim slot for a ~7€ data-only plan from one of the discount MVNOs just to avoid being caught in this situation.