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Neither a bad O2 or a clogged catalytic converter should be able to cause this at all. The downstream O2 doesn't affect engine operation at all, it's just an emissions monitor to trip a code.
A shop with access to a scanner with a graphing function (not necessarily HPTuners, but there are other basic scantools that most shops should have) can show how the O2 is fluctuating, and you can see how it's acting when it's plugged in. See if it's hanging out way too much on the lean or rich side, or the graph is going crazy.
Bad cat will make it feel like the car has no power, but it's not likely to generate misfires like you're describing. And if it were a bad cat, it wouldn't run better with the O2 disconnected.
Seems to me like a vacuum leak. Check the hoses (especially that MAP one, if you haven't replaced ever, well, every 2.4L I've seen has had that hose super cracked this far into its life) and you can spray brake cleaner when you first turn the engine on around the intake manifold gasket area (so it's relatively cold still) and you should be able to tell if there's a leak by the way the engine reacts. (do it with the O2 disconnected)
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