Snikket is an attempt to solve the XMPP issues, or at least to reduce them, single all-in-one XMPP server distro and clients across platforms, and since it's self-hosted no one should get their hands on your data (in normal circumstances).
That said, the saying goes "Perfect is the enemy of Good". Just because a solution is not perfect doesn't make it unusable, any of those options you mention full of problems are a helluva better than FB Messenger or plain SMS for example. Depending on your threat model they might be more than enough.
About Appraisal Isekai Season 2, been following the manga, and we're about to enter the actual succession war, so here's where both most characters will shine, and where it will go most Suikoden with the recruiting people thing, high hopes here