Yes. It's the classic argument that less tax leads to more economic activity. That argument is dubious at times, and I doubt that going to 5% would be worth it, but it seems highly likely there would be big upside (to Apple) by lowering it.
You could do a lot with even 15% more revenue. It's not like app developers will go pocket it. What a ton would do is go buy ads (from Apple other others) to drive more app adoption, because they're already doing that as much as the margins support. Or they'd invest it in the thing that drives value for the app. (E.g., Medium would invest it in content.) Which ultimately benefits Apple, as well.
Then there are whole large businesses — like Netflix and Spotify and Kindle — who have decided it's not worth it, who they might be able to retain. Would 10% of those app's revenue be worth 20% of millions of others? (Yes.) Not to mention there are businesses that *could* be built on the platform that aren't even attempted today because they don't pencil out with a 30% tax. And lastly, there are businesses that might be able to make payments work instead of ads. (You don't pay the tax if you're ad-driven.)
I'm sure there's a counter-argument (besides short-term greed?) but it's hard to fathom. I'd love to hear the analysis inside Apple on this. I'm also surprised Google does the same thing (with less flack) rather than lower the fee and incentivize developers to favor Android.