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Did a VERY lazyish test, but it looks like the boost from Dragon's Maw is about 30%-40%. No hard numbers, but probably close. Smacked a Claydoll with a Flygon then Regidrago. Their attack stats were pretty close, and it looked like Drago did about 30% more than Flygon. Don't take this as a hard...
I'd argue OG Articuno didn't have garbage stats, so much as the typing just counteracting what bulk it had. 90/100/125 was good bulk, and arguably still is. 95 special attack isn't great, but it's just enough to be OK. But Ice is such an awful typing that it undoes all of that. Especially since...
Awful how? Blaze Kick and Stomping Tantrum would cover what it can't use its STABs to deal with. Fighting/Flying isn't even bad coverage to begin with.
It still is. And, good thing, you can choose not to keep the pokemon and you'll be given the option to specifically hunt it down later. Just gotta talk to the scientist lady. So no, it's not a big deal.
Curious to see how the Ice riding form fares, since it's got a bad type combo and is still very slow. But its stat total is still pretty bonkers for a place like OU.