Whether or not you "do intense graphics" is no argument to avoid getting a graphics card. Your computer does graphics for nearly every program you use. Graphics are almost exclusively the single most processor intensive part of a program.

The money you sink into your graphics card is literally taking the cheap route to letting your CPU handle the things you want it handling, while not handling the graphical stuff, which it is not optimized for anyway. It's the cheapest way to get faster performance out of your CPU so that it is doing less stuff, but focusing on the stuff which you perceive as causing "laggy" moments.

A GPU is a parallel processor. It's designed to do the same process to many chunks of data.

A CPU is a serial processor. It's designed to do a different process to each new chunk of data.

Having a dedicated GPU is nothing like choosing a single or dual core. That's just adding another of a part you already have. The GPU is a different part that does different tasks.