My two cents based on my experience:
Getting my immediate family to switch to Signal was relatively easy. Since many of them rely on me for tech support, getting them to add another app to their phone was not a problem since I “manage” their devices for them anyway.
With friends, it gets harder. Close friends will usually add the app and I found many of them actually do like Signal because it is a cleaner messaging experience. Signal users are not the type to send random forwards and there is no scam/spam like there is on Whatsapp. Regarding additional benefits that Signal has over Whatsapp, many of the benefits are technical and won’t be enough to convince a user to switch. Open Source, Minimal Data Storage, Non-Profit Organization – most users don’t care about this.
So my solution was not to leave Whatsapp entirely, but to install it on a second phone. That phone has nothing on it except Whatsapp. If anyone messages me on Whatsapp, they get an auto-reply informing them to expect delayed replies as I do not check my Whatsapp regularly. If they want a fast reply, please message me on Signal.
That way it’s more of a soft sell and you are giving them a choice.
By the way, there is a way to use iMessage on Android phones (messaging only, no video or audio calls) in case you did not know. And if you want to check Whatsapp from your primary phone without installing Whatsapp on it, you can use WhatsApp Web To Go on Android.