I'm wondering if it would be worth it to power up raikou with anything beyond the candies from the pinab'd research catches (a possible raikou raid day likely wont come for another 3 or so months). I looked at current and past raids and defenders to see its matches
When it comes to flying types, the only ones that are in gyms most of the time are Dragonite/salamence or gyarados, and when gen IV comes out, likely togekiss. Against the dragons, tyranitar handles them much better without the cost of rarecandies. Against Gyarados it goes through it extremely fast, though thats only due to a double weakness that any electric type could take advantage of without the RC cost. Now against Togekiss it would be good, having 2 dps up on tyranitar and not having the weakness to fairy, but that on its own doesnt seem to justify the RC cost. With a projected Moltres Raid day coming up, Tyranitar would take the lead (and also be good against Entei if it ever gets one) and agaisnt a possible return of lugia, it only manages to eek out around 1.1 dps on Bite/SE tyranitar.
Agaisnt the water types, it is the best against kyogre and Suicune, but with the exception of Blizzard Kyogre time's tamed both of them, with alternatives becoming much more viable withought the cost of the rarecandies. Agaisnt Suicune (who likely also wont come back as a raid day for a while) PF venasaur only looses about 1.7 DPS. For three man'ing those two, raikou would be necessary, but they aren't currently in rotation and likely wont for a while. Electric is good against the numerous former raid bosses, but as most of them dont come from Johto, and the johto event will be starting soon it doesnt seem likely that any beyond Azumaril or Croconaw/totadile will be coming. As for the numerous ice/water types, machamo does better against them than Raikou, having more DPS (though raikou has more TDO, but does cost rarecandy)
However, theres on thing I haven't mentioned yet, which is rain. Its a very good generalist in the rain, but outside of that, super effective counters will do better. (even in the rain, when against dragonite, Tyrantiar beats raikou)
If PvP is added, Raikou will likely become better, matching 2 common tanks, kyogre and Lugia, but how PvP is implemented is still yet to be seen.
It doesnt really seem like Raikou, the ones from the breakthroughs at least, are worth powering up because of what the rarecandy cost would be in relation to what Raikou matches that others cant. Is there anything I missed that makes raikou more worth powering up?