1- The team is formed with people who play arena 5+ hours a day. If you queue enough , you will eventually have a session where counter comps are offline. How do I know? Because I face the comps you mentioned all the time, they lose miserably due to comp and they don't have decent mmr, I don't get to face them other days because I don't play as much and when I check the ladder next week, I see them in top 30.
2- Sometimes, those teams have 3 amazing players, so they manage to do good. Ex: s12 mirlol rmp at 2500+ or so.
The comps should not be evaluated over the results of world class players or no life arena queuers that ended up having a decent session due to no counter comps showing up eventually.
So excluding few exceptions, people who don't play with amazing partners, will have really hard time if they don't play a T1 comp, that has always been a problem in wow arena, but right now it is at its worst state because the damage and instant cc doesn't allow you to play "much better"