That's a statement about zoo in general, if you build any board against them that they can't deal with the next turn, they already lose. The problem in the shaman match-up is that overload doesn't allow you to follow-up so baiting out early removal that overloads them is great. Lightning Storm early is also good because it most of the time it will force their next turn to either be nothing or just a totem which is a win for the zoo deck.
Shaman actually has great issues against Zoo, you need to get a bit lucky with draws from both side. Honestly more in favor of Zoo because Shamans just aren't great at dealing with lots of early pressure unless they draw perfectly against the Zoo's draws.
I would say not to even make decks vs Zoo though, but focus on learning how to shut down Zoo by learning what cards are useless in the match, knowing how to mulligan and when to drop cards to basically die to delay damage so you can stabilize for later. Druids are super strong against Zoo and Handlock which helps, but regardless of what class you play, it's good to analyze how you can manage the opponent each turn. If you basically do nothing in a turn against Zoo, chances are you're probably dead.
Depends on the overload. By the time some cards become available, the overload can cover its cost going into the next. If I lightning storm off 3 one-drop minions, I still have 2 mana. Lightning bolt, forked lightning, etc can still be done, and when the warlock is down to basically dipping for another then the shaman can roll. Overload isn't the end-all, as I said it can cause problems, but it does make the warlock stop and play his own cards carefully. If you spend time baiting for my removal, I can just build my board until you don't have a choice. If you try to pounce on my field after one spell, and don't pay caution to the next spell on its way out, then you have trouble. Its all on how much the warlock can afford to spend, and if he just hams out to try and take advantage of a storm that came and went or isn't coming, the shaman has his ample time to set up.
As far as the "shamans aren't great at dealing with lots of etc", eh, I'm not so sure on that one but we can have our separate opinions on it.
Yeah I agree not to build specifically against zoo (since for the most part, anything that beats zoo loses to miracle), however I feel like one can construct in a way that makes them strong against zoo given their assets. Zoo has two main things about it: Lack of big removal (things that just outright kill something, like assassinate, poly, or hex), and a dependency on low-cost board dominance with their only real draw engine being a 2-2 for 1. I feel like Shaman is pretty well equipped to deal with it, and I happen to play druid so I know about that line of it. I even enjoy warrior against it because if you can outlast that initial onslaught then you're practically golden and they have a lot of 2 and 3 damage tosses that they can live without.
To be fair, I run a certain kind of druid and "mana wraith" is a part of it. Having the minions cost even 1 mana more kinda spoils the stew for them in a big way.
