Are you agreeing with the OP who didn’t see any point and advocated that GrapheneOS “totally ignore RCS”

No. I think it is useful for GrapheneOS to work on this, the US is a substantial user base.

The comment I reacted to:

iPhone users very often don't want to have SMS/MMS users in their group chats.

I think it is useful to qualify that, because a lot of people from the US are under all kinds of false beliefs like: green bubble anxiety is universal, Pixel 10 and Pixel 10 Pro do not support physical SIMs (Pixels support physical SIM in other regions), etc. (I could go on for a while.)

These misunderstandings repeatedly show up over and over again and discussions, so I think it is worth being specific. In this case most iPhone users worldwide do not even think about SMS/MMS users in their chat, because they do not even rely on iMessage as their primary messaging app.