I also use WhatsApp and Signal as a daily driver. iMessage is legitimately superior to all other messaging platforms I've used, and it isn't close.

iMessage isn't just a text messaging app, it also serves as a shared application fabric. The many iOS objects and apps are integrated into iMessage as first-class things that can be securely shared and seamlessly collaborated on between groups of people over the iMessage backbone. It isn't just group chats but also group content. If you have non-iMessage users in the group then all of this is disabled and it reverts to being a text message app. I know many average people that live in those collaboration features without even really thinking about it because they work so much more seamlessly than the alternatives.