Arduino is added complexity. In my limited hobbyist experience, going to the datasheets and using official toolchains has been very straightforward. It pays to build the understanding ahead of time rather than debugging some random person's Arduino library when your peripheral stops working.
Arduino's added complexity opened up the space to people who had little-to-no programming experience. People who had a computer with a USB port. People who had no familiarity with binary let alone hexadecimal to set a bitmask so they could turn an LED on. Let alone figure out which bits to flip to set a timer.
Arduino is added complexity to the benefit of accessibility. The complexity of the datasheets and toolschains make most products an unassailable wall. That said, the real gem of Arduino is its community that is welcoming and helpful to beginners.