Ah, the outside offer is an absolute game changer, which IMO puts it in the same league as actually changing jobs. Often you have to show that you are willing and able to leave for a much better salary to actually get the much better salary.
If you are just internally lobbying for a salary increase at your existing employer, regardless of how successful you may be, how much revenue you are bringing in, etc. I would say at the vast majority of companies you will not see nearly the same raise as either presenting a compelling outside offer, or actually taking an outside offer.
Another way of thinking of it is that a company cannot pay their employees an arbitrary amount, it has to be justified up the chain, and usually that justification is based on "grades" or "scales" of some kind or another. Most of these scales will include a fixed range for annual raises. By bringing an outside offer, you are providing the necessary documentation that your manager, HR, all the way up the chain is required to actually sign off on the raise. The outside offer means no one is sticking their neck out to justify an out-of-spec raise, or claim someone was being previously underpaid, it's just a simple equation -- the employee has an offer, and the company can make a counter-offer or not.
Of course the trick is if they decline to counter, or counter low, you have to consider if you then leave, or stay? You also probably can't come back year after year with new outside offers, it's a trick you can only turn to so often.