You can actually do a soft transition from the (opaque) Arduino programming style to a programming style closer to hardware. After all, Arduino programs are just C++ and you can plug in your own functions and assembler and you can even compile and upload your own ASM/C/C++ program written from scratch and compiled with the gnu-avr-toolchain to the UNO.

After you have done all of that it might be a good idea to start soldering the AVR on your own boards.