This is not exactly correct.
First question, the usb type-c can carry analog audio through its pins, the iphone lighting connector no, it is only digital, for this reason the usb type-c can use the dac and the internal amplifier of the smartphone and the cable is a simple connection cable, on iphone this is not possible, the lighitng and only digital, dac and amplifier must necessarily be integrated into the cable.
Second question : the sound quality depends on the dac and the amplifier regardless of whether it is in the smartphone.
Third question : Not having the 3.5 jack is inconvenient, you always have to remember to have the cable with you, for example if you listen to music on good headphones and the next day you forget it at home, you can not connect any headphones to your smartphone, for this I have an iphone 7 plus, in addition to the connector in the package I bought a Fiio I1.
Then there is the problem that you can not recharge and listen to music at the same time