I haven't tried the iPhone 7 but I'm sure that it offers decent audio. An inexpensive DAP will have at least the equivalent in audio quality and often significantly better output power to drive a wider variety of earphones and headphones, depending on the model.
But wait, there's more.
1. How much does an iPhone 7+ cost? Decent DAPs like a Benjie S5 cost $30. A better DAP like a Benjie T6/AGPtek Rocker costs $70. A next level up Fiio costs $150. You can buy DAPs that cost as much as an iPhone, but you will probably find that an inexpensive DAP makes more sense for portability and value.
2. I pay $5 a month for phone insurance, just in case I need to replace. I wouldn't buy insurance for an inexpensive DAP.
3. A DAP does not need replacement or upgrading every two years. A firmware update keeps a DAP current but you probably don't even need that for any device that has been on the market for more than a year.
4. I constantly use my phone for work and I need every bit of battery power for use and reserve. DAPs run for 8 to 40+ hours and you don't lose a deal and your job if you inadvertently drain your battery.
5. You get much better sound by using headphones with a corded connection. Does the iPhone still have a physical audio port?
6. DAPs almost all offer FLAC file compatibility and the better ones offer DSD and other lossless formats as well. Apple has some lossless file compatibility but keeps pushing you toward the Apple Store.
7. Large music file collections require lots of storage capacity. I can swap in 256GB microsd cards that cost me $20 in 5 seconds. How much does an iPhone 7 with 256GB of non-swappable memory cost again?
8. As to having to carry two devices, the smallest DAPs really are miniscule and can take a beating. I drop mine in my briefcase or in a jacket pocket and just leave it there for when I need a rock 'n roll break.
AGPtek is sending me five of their DAPs to demo, so try 'em out at the meet and see if they make sense for you!