I don't think this is the correct way to get a good bokeh. What you are getting here is an OOF image. Try to take something close at f2.8 in the daytime and then see if the background is what you expect it to be.
Well, technically bokeh is background blur, so what i'm doing is simulating it. My 75-300 f/4.5-5.6 can produce a nice uniform circle without the dot in the centre. I'm wondering if it's a lens fault?