One of my partners and I try to speak for one hour each time. We schedule one half hour for her to teach me and the other half hour for me to teach her. So far it is working well.

It can't be helped. For example, English and Japanese, well, I guarantee the conversation is going to be full of English, so don't blame them, they're not selfish, they just find themselves in an awkward situation and think "what am I even doing here?" in their head.

And yes, it's indeed a lot better if it is your friend in real life.

Language exchange by speaking in person is a waste of time in my opinion. First reason, no topic to talk about. Second reason, It's not like your partner will stop and tell you every single thing you don't understand and even if they do, they need to have a really good knowledge of your native or whatever language that you're both good at or they will just find themselves struggling  to try to explain what you want to know. And even so, you're not going to remember them all unless you actually write them down. But well, a conversation with paper and pen or whatever and both parties have to explain so much is already beyond awkward. And of course, if the conversation goes smoothly, then it means your skills are already good, if that's the case then it's pointless to start a "language exchange" because it's more like a "language review", and again, in this case, back to the first reason, it's not like you have much to say anyway. "enjoy talking with you"?? I'm sorry but you never enjoy talking with a stranger, especially when you both have nothing in common.

The best way to fully master a language is to learn it by yourself or go to a country that uses that language. However, your skills need to be really good already or you won't be able to adapt. Living in a particular country never helps you improve your language skills if your knowledge of that language is low, it will just backfire. Of course it's not the case if you happen to be sent there by your parents and already have everything you need to live there including occupation, money,...etc.

Well, I find that it takes some time to find a good fit...sometimes people think that they want a language partner, but then they freeze and are scared and quit.  I found one partner...20 min in French, 20 min in English, each responsible for the topic in the language being learned, so I choose topic in French, he chooses topic in English.  We've been talking for close to a year.  He tends to take over, so I have to remind him of our ground rules every now and then.

remember that everyone learns differently, so language partners work for some, not everybody.