The difficulty setting makes a big difference.
I won't say it's a masterpiece of encounter design. But on higher difficulties almost every enemy has a type of shield and they use their powers more.
Efficiently clearing a room requires smart use of weaponry and/or powers as well as combos with your squad. Aka, using your powers on cooldown, always.
I'm not going to say Alex plays wrong but with his playstyle he should really just have picked soldier, as his abilites would actually complement his playstyle.
The sentinel shines in CQC where you use your armor exploding offensively. It also requires squaddies that can trigger you lift/ combo with shockwave. Squadmates abilites don't need to arc, so those will always trigger the explosion when primed.
With a controller you need to pause semi-frequently to do this, but that makes this easier instead of harder.
