Usually the main tank does not stun, it is the off tanks duty to stun. When you are first learning a fight you might need to just sit there and auto attack so you can have your gcd up to stun the move you need. As you learn the fights, you'll know around what time the abilities will be used and can weave whatever skills in that you want during the meantime. i do think it kind of sucks that someone basically just has to be a stun mule but i guess that's how it goes. If you are running with a group of friends however you can easily coordinate stuns/silences so that you are not the only one doing it.