Of course I keep meeting players that express their upset feelings (and it can get pretty colourful sometimes), sometimes they are trying to give me helpful advice when I ask what I could improve on, I end up in the higher spots of damage dealt (MNK), but it just needs one guy to kill your mood and motivation for the gamemode.

You play with someone in a small team of 4 people, every player is important for the outcome. And then you have one or two in your team who don't know what the hell they are doing or are not aware of how to handle specific matchups (if you are a newcomer to the feast, how are you supposed to know all of this from the start, it's impossible).
You obviously get frustrated because you see the mistakes they do, they don't, seems so obvious.
Because you are not new. The community is almost entirely only out of veteran PvPers that have been doing this for quite some time. Which is not a bad thing, most of them are trying to improve and revitalize the community.