Yeah, so, the problem is that mons generally have to live a hit from the mon they are meant to check in order to check (provided said mon outspeeds the check, which Doom does for both Clef and Argho). Please see the calcs that were in reach's post that I have quoted below.
Clefable only has a chance of living a +2 Shattered Psyche, and that's assuming Timid, or SpA neutral Nature. If Doom was Modest, that thing is dead. Psyche also easily does the same on Argho. Now look at the speed. Clef is base 60. Argho is base 75. Doom is base 110. For those aforementioned calcs, the sets were defensive. Doom is naturally going to be running a large amount of speed itself to make the most out of its high base stat. They are not outspeeding Doom. With that, please explain to me how, in any manner, Clefable or Argho both plan to live an already set up, +2 MB Voodoom's attack in order to fire back one of their own STABs. It simply won't happen.
I understand you just want to help and are new, so let me explain where I believe your thinking went wrong. Ideally, yes, checks are meant to have free switch ins to be effective. However, if Voodoom is at +2, which only takes one turn with Nasty Plot, they cease being effective. Thus, they can be deemed checks only for a +0 Doom. Unfortunately, the first thing a Doom is going to do in a realistic situation, is switch in on something it can set up on, and then set up while you switch out to whatever you feel is the best check/counter. Of course, this opens up the opportunity for predicts and all that jazz, but at the most basic level, Voodoom has the option to very easily get to +2. As a result, that means that Clefable and Argho very easily lose their check status, since they only function at +0 for NP Doom.
Now, if you say, "Well, then don't give Doom psychic coverage and it won't have Shattered Psyche." The problem is that we're not looking at nerfing this mon, and since it already has Psychic in its movepool, the move won't be thrown out just for the sake of making an extra, highly debated update work better.
As for what I personally favor, I lean with the no Comp. Ability crowd. It does bug me greatly having Volt Absorb and whatever Hidden Ability we choose to both be wholly niche/flavor, but I honestly don't currently see something presented that makes me think "Yeah, Voodoom would be better with this, but not to a point where it's overbearing."As such, I lean No Competitive Ability.