It is. It's much more than "mages with a shield". It's a tanky swords(wo)man with defensive and offensive magical abilities. You can equip the mage staff and cast regular mage spells if you want, but I prefer the sword/mace + magick shield combo. With your sword/mace, you can do things like setup a vortex that draws enemies in and damages them, or setup a sigil that staggers and damages all enemies that walk in it (it's juggles them hilariously, tons of fun), or a ball of light in front of you that you attack which will then throw more balls of lights and the enemies around you.
The magick shield abilities are also fun if you like to do perfect parries. For example, an ice-buff shield, when performing a perfect block, will freeze the enemies in place, leaving them vulnerable to a devastating counter-attack. And you can also do various other defensive and offensive buffs with them.
Edit:
Holy cannon (the ball-of-light ability described above) is the only ranged ability of the Mystic Knight, as far as I remember. For a primarily melee class with magical ranged support, I suggest Magick Archer. Melee is gonna be daggers (warning, you can't block, but you can dodge roll at least), with some truly strong melee options too, and the magick bow abilities are among the most fun and spectacular in the game. It might seem a bit weak or underwhelming early on, but later, like in hardest area (the DLC expansion area), Magick Archer is the best class by far.
For melee/ranged without magic, strider and ranger are great too.