If you are counting to use less skills than necessary, then it will not be your best choice to play a tank.

Rotating deffensive cooldowns is a core of all tanks skills, necessary to make run as easy and fast as possible, without it you are going to fail misreably. You will have to know which skill does what and use support abilities in order to help healers not failing the duty away.
You still have to do your DPS rotations properly, you use most of your offensive kit in duties anyway, those could take up to 16 - 17 buttons alone.
On top of it you have some necessary role actions to use as well like arms lenght, rampart, low blow/interject (for stunning large aoes on mobs), because you will find yourself having to use everything you have in order to keep yourself alive.

DPS is an easy cake in comparison.