Black Knight Irios
Explorer
I see no reason to give a proficiency bonus to implement users. As others said, NADs are usually 2-3 points lower than AC and if you pick your powers wisely you can target all 3 NADs as you need it. And sometimes the difference between AC and a single NAD is more than 5. That is roughly the same as a weapon attack with prof. vs a NAD.
Nothing more to add.
Well, this is easy... no, implements should not get a proficiency bonus because they target defenses that are lower than AC.
Other powers getting an effective bonus to attack because they get proficiency bonus and target other defenses isn't particularly material, anymore than it is for powers to get bonuses to attack (Sure Strike, Mesmeric Hold, etc)
Ie, it's okay for Piercing Strike to attack Reflex with a prof bonus in the same way that it's okay for Mesmeric Hold to attack Will with a +4 bonus.
Nothing more to add.