Pick one of your latest images, click on it:
What size do you have on “Original” as seen under “All sizes”?
(“All sizes” is clickable just above the image)

I’d say that too small size on uploads might be one limiting factor.
I believe uploads needs be at least 1024 pixels wide or high (largest measure).
Why: Because the flickr automatic downsize needs data to work on, it can not enhance what you upload.

Mine are mostly resized (downsized!) as close as possible to 3MP  (e.g. 2100×1400 pixels for 3:2 or 1775×1775 for 1:1 as width:height ratio).

Also, shooting with

  • relatively large aperture and
  • long focal length
  • at short range

… will have your camera fight with focusing right, as this means a shallow depth of focus (due to basic physics/optics).
Add low light and you are very close to the limits, either very high in ISO or at long shutter speeds.
A not so sharp lens on top of this and you might miss an opportunity or two…

You don’t have to tell me, you know what you have – and what you can do about it. I’d say it sums down to:
Either live with what you got, or look around for something suitably better – limited either price-wise or performance-wise.

Perfect images require both skill and a suitable equipment, one cannot create wonders.