Not all people are rich enough to have iPhones. And if you really want privacy, you wouldn’t go for one anyway, instead choosing Graphene/Divest/Lineage. Not to mention iMessage is fully closed-source so you cannot even trust it to do what it does. I have issues wirh Signal, but at least I would take it over iMessage any day.
I used to use Vanced but switched to Newpipe, as it is noticeably lighter (also at least for me, downloads did not properly work while they were fine on Newpipe).