First of all, VGC and LC aren't calculated in his blog posts. They are so radically different from other metas that they should be formula'd differently.Read through all the blog posts and this thread. Interesting project, and cool scatter plots. Mostly looks very good, though there were a few things which seem like they may be questionable. If you're not keen on revisiting things that's fair enough, but my thoughts:
Why exactly do you feel LO should have exactly the same effect as Choice items? From my experience Choice users tend to be more wallbreakers than full sweepers, and unlike choice items Life Orb has a significant direct harm to the holder's defensive ability. My gut feeling is to give LO a higher rating, though I'm not entirely sure about that.
Second and much more major point, you seem to be discarding the lower offensive and defensive stats entirely.
This will mean your formula cannot take into account the advantages of being a mixed sweeper, or, more importantly, the fact that some Pokemon may have one decent defensive stat but be extremely frail to the other kind of attacks (Cloyster, Aggron, Blissey, and Mantine are excellent examples, but even more mildly unbalanced defenses will cause a Pokémon's stallishness to be overestimated to a lesser extent). I can see why you'd want to make that simplification, dealing with both stats can get kind of messy, but this seems likely to be the biggest issue with your formula's correctly assigning stallishness from stats. For attacks perhaps raising both to a power, adding them, then taking that power's root of the result would be effective? A larger power would mean a smaller boost for mixed attackers, and visa versa. Ideally this would only be applied if the set used both physical and special moves. A similar method (perhaps with a different power) could be used for defenses.
Doing this may complicate the effects of certain items. In particular, Eviolite and the Choice items could no longer reasonably said to grant exactly the same boosts. Applying the item boosts in the initial calculation would solve this. And doing the same with Life Orb changes the previous point, applying the boost to both stats then having a smaller modifier simply from HP loss which is near equal or equal seems sane.
Generally a good idea, but I'd suggest some change to how healing berries and berry juice are handled. In LC holding an item like that gives a massive boost to endurance, even though Eviolite seems much more popular in 5th gen and Berry Juice is banned from both. Making these items have the same effect as Salac or a Gem seems backwards. I'd suggest making one time use items which heal health either have +0.5 or at least be neutral (also helps with VGC/doubles/triples, where Sitrus is somewhat viable, and clearly more defensive than other one-time use items). Status healing berries are more debatable. They're used with Rest for one time healing, but of course that's still just a one time thing, not full stall's style, but also not hyper offense style.
Halving the change to the metric because of a fairly small difference in health gained, when it can be activated on the switch rather than needing a turn to just heal.. hm, maybe it's not quite as stally as others, but 0.5 does seem slightly low.
Also missing items which seem possibly worth considering:
20% type boosting items and plates
Wise Glasses and Muscle Band
Most species specific boosting items (Soul Dew, DeepSeaTooth, DeepSeaScale, Light Ball, Thick Club, Adamant Orb, Lustrous Orb, Griseous Orb, and maybe Ditto's two, Lucky Punch, and Stick?) when held by the correct species
And to generalise this to all generations, maybe Berserk Gene?
Eh... I think Life Orb is less offensive than Choice Band/Specs, and more offensive than Scarf. This is going on the power output alone, but it's certainly debatable.
Expert Belt and Species Specific Boosting Items(SSBI) These really should be in there. EBelt is a very viable item that shouldn't be ignored(especially with Genesect just being released, and the SSBI are HUGE differences to a pokemon's playstyle. THe best thing to do here is to calculate them with the same level as the moves they imitate(i.e. Soul Dew=Calm Mind, Thick Club=Swords Dance). Certainly the easiest thing to do.