These engines are complex so proper diagnosis essential hence Vida, however there are some basic checks you can do e.g. ensure all vacuum pipes are attached and no obvious leaks, but more importantly is the bottom turbo hose intact - can you hear any hissing when revving and getting the turbo to kick in . - many posts on this fault which causes massive power loss.
As you suspect, swirl flaps cause some small issues but not a massive power loss; you might be in limp mode which I think can only be reset using Vida as happened to me when car in accident and garage disconnected ECUs at some point and car then went into limp mode when I got it back.
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