The Double Irish + Dutch is merely the most extreme example of the transfer pricing morass (and will go away in a few years). There are a bunch of other funky methods described in the wikipedia article I posted on the topic; defining and proving in court that a particular method of determining "market rate" was unreasonably chosen and incorrect enough to be worth the trouble is quite involved and, in normative terms, a big waste of economic potential (brain power on both sides is devoted to … that, rather than something useful).

As for "taxing IP licenses at the corporate tax rate", that seems nonsensical given that it's profit (aka value added) that is subject to tax, not revenue.