I'm assuming the fees stack on top of the savings from using BNB? I went ahead and bought a bunch of BNB a while back just to make sure I didn't have to worry about that anymore. If the fees stack on top of what you get from paying fees in BNB, it may be worthwhile to go through the whole account creation process again if you do a lot of trades.
It works on top of the BNB savings indeed. You can see the full overview here:
https://www.binance.com/en/fee/schedule. Using the 20% discount you'd be moving from the second-to-last column, to the most-right column.
(not sure if my account allows to paste an image, but here is an image url:

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