SMS is insecure as hell, RCS suffered from issues between Apple and Google, both were limited for a long time by Telecoms and priced too high after reaching your allowance (i remember my first mobile contract having a whooping 10 SMS/month included). The amount of data messenger apps use is negligible even with pretty low data limits as long as you are not attaching whole movies.

I personally only use Signal - i have removed all Meta products from my life. If someone without Signal wants to contact me, they can use snail mail, i really don’t care - i won’t sacrifice my privacy for the convenience of others.