Thankfully, shit like this will soon be illegal in the EU when the Digital Markets Act hits. Hopefully they'll plug all the loopholes and actually enforce it. I don't understand how anyone can defend business practices like this, which are exclusively there for the purpose of platform lock-in.
I think Tim Cook is spot on here. Get an iPhone for your grandma if she wants the user experience that iMessages provide. Otherwise, you can get her signal or snapchat or one of the 4,225 secure messaging ecosystems.