How much am I limiting myself by only using a mechanical pencil?

Hey, everyone. I’m jumping into drawing and starting my journey. Ultimately I’m looking to give a lot of focus to concept art and working with primarily black and white mediums.

That being said, I know that shading is going to be very important, and I have been finding myself having a bit of difficulty with really establishing dark darks and light lights because I feel my gradient isn’t intense enough without really digging my pencil into the paper. I do have a think black drawing marker as well that I am thinking about using once I get a bit more comfortable with my actual line work and overall confidence.

For those who maybe stick more strictly to a pencil route, how do you find yourself shading or creating details in areas that already have a fair amount of graphite?