Let's not forget that the prime function of any chat is to be able to reach out and to connect other people. What is a point to use unpopular apps, which are used by less than 1% of your contacts? It's usless. So the good chat is a popular chat in the first place. Just whatsapp and skype can encompass 70% of the earth population. And if you need some specific markets such as China, Thailand or Philippines, you could always add relevant apps such as wechat, line, viber to be covered completely.
IMHO it's a mere bs to overthink regarding security. All popular chats are encrypted and secure enough to keep your conversations private. If you are someone like Pablo Escobar and one day CIA decided to track you down, "secure" chat or protonmail wouldn't help you.