I am rather confused. You say you play with a hunter and a rogue and you eat cc the whole game and then someone replies that shadow priests are bad in 3v3 due dispel los. I will assume you play discipline and that the fellow shadow got confused?
Well from what you described it seems like your partners are afk. IF you get on CC chain tell your partners to stop that cc chain. You can avoid poly and blinds by using SW
? use fear ward when priest comes close to you? BE more specific in terms of what short of cc chain and what team troubles you most so we can discuss further
Are you talking about end gaming play here? Like 2800MMR+. I play shadow priest not very high I have to admit (I am between 2300 and 2400MMR) as shadow play and Rogue-Shadow-Shaman and I totally disagree with you. If a melee can trinket your disarm then dont disarm someone who has a trinket up. Sure you cant dispel nova's anymore but you can remove a mage's cc easy (life grip on DF/RoF? mass dispel poly?)
Getting tunneled is quiet true, personally after dispel Loss I run 4k resilience with 2 Satin and 3 Mooncloth, I use fade to get away and get the necessary peels when i am out of trinket or disperse.
Lastly in the case you refer to TSG tunneling I do no know what short of combo you play but have you tried Disarm, Into Deathcoil with full row of dots on warrior the moment he pops releckness?
I do not want to sound like a dick or antyhign and theory is easier than practise, but shadows are viable. Maybe not glad rank but defo 2400-2600+.
My 2 cents, noone has to agree here.