As an instruction set, yes, but I think this was inevitable with the demand for things like native USB, Wi-Fi, Bluetooth, and hobbyists wanting to use languages like Python. These boards do a lot more than the ATMegas I grew up with, and while almost every new design in this space might go with ARM thanks to generous specs and low cost and power requirements, I think there's still a good amount of competition in the 32bit microcontroller market (ST, TI, Microchip, NXP, etc. come to mind).