One of the reasons I think that Conk is so dangerous in this current meta is that with AV he's one of the best existing checks to Thundurus(thundurbolt is a 3hko), Heatran (can't burn, fire blast/flamethrower/lava plume are all 3hko's) Sure he lacks reliable recovery, but he has better reliable recovery than every other Pokemon in A+ rank (excluding Mega- Venu, Talonflame and Kyu-B. who all get a 50% recovery move). 7 out of 10 of the mons in A+ rank get worse reliable recovery than Drain Punch provides Conk with. Therefore, I think it is a flawed argument to say that Conkeldurr shouldn't be A+ rank simply because he does not get the most reliable recovery available. Especially when his recovery options are greater than 70% of the A+ section.
I think he would fit nicely in the A+ section because of the power he has to make people think twice about switching, and his ability to check top threats this gen such as Thundurus and Heatran, which I mentioned above.
Conkeldurr suffer from quite an ammount of problems though. .
First off, it gets worn down very quickly, due to lacking reliable recovery (DP isn't very reliable, when facing a low health opponent or a poké with low HP (see: Rotom-W) it won't heal a lot) and guts.
On the subject of Guts, 99% of the time it HAS to be your ability, or else you get crippled by will-o-wisp (and Rotom-W being everywhere doesn't help Conk) and you gain nothing from toxic, not to mention that paralysis is a thing.
Also, it's power is quite meh, lacking a boosting item or a boosting move due to AV, when topped with the relative low power of his moves, just doesn't cut it most of the time, with Conk having to rely on SE hits and Guts to patch up it's disappointing power. It's low speed haunts it too, it just can't retaliate against fast foes that have enough bulk to were Mach Punch doesn't really harm em', or simply resist the move, and can 2HKO, or with prior damage, OHKO him while he can't do nothing.
And finally, like many said before, the meta has adapted to it's AV set, which based your promotion to A+ on. Special attackers like Greninja and Landorus-I use Psychic type moves to deal with him and other pokes like Mega-Venu, and Talonflame is a thing, and Conkeldurr just can't deal with it. It also has a bit of a 4MSS, the most common set is Drain Punch/Mach Punch/Knock Off/Ice Punch, while this is fine and dandy, it can't deal with most fairies, it can't, some examples:
Sylveon: Can easily chip him down with Pixilate Hyper Voice, and Drain Punch doesn't heal enough, ice punch doesn't do enough
Togekiss: It can ice punch, but it can paraflinch him to death
Azumarill: Eats anything, outspeeds and kills with Play Rough
Clefable: It can just set up it its face
While Conk has Poison Jab to deal with them, then comes the trouble. It NEEDS Drain Punch because it's his most reliable STAB due to recovery, it needs Mach Punch necause without it its useless against faster foes, Knock Off deals with any Psychics and it's too useful to pass up, and Ice Punch allows him to deal with flying types, and pokémon that will normally wall him to hell and back, such as Gliscor, Landorus-T and Hippowdon, to say a few, so it's a hard choice, it also has Rock Slide to hit Talonflame on the switch and get rid of it's biggest fear, but that ain't as important.
Honestly i'd say AV Conkeldurr isn't as good as people made him to be once, as the meta as adapted to it, and it doesn't hit hard enough, it's pitifully slow, and it can easily be worn down. Also other Conk sets such as Bulk Up and Sheer Force attacker are definitely not as good as they we're last gen (heck, even last gen Conk was C+) due to it's pitiful speed, lack of special bulk, and there being better attackers out there, overall, i'd say Conkeldurr is in no way derserving of an A+ rank, and an A one at that. I'd say B for it