Seems to me that, aside from telling you to add ingredients (I am going to assume that you added salt prior to adding water to help sweat the ingredients), you may be missing the step of fully preparing your stock. While browning your onions will have been effective; did you just add the carrots along with the water, did you give them an opportunity to sweat and brown as well?
- Be sure that you allow the onions to fully brown. This will ensure that they have expressed their fullest flavor
- Be sure that your carrots are being steamed (covering the pot with a lid is very helpful) and then cooking fully to create your stock
- If you added the carrots and the onions at the same time, but the onions are browning sooner than the carrots even get soft, add some water to the bottom of the pan to prevent the onions from burning, but to keep the carrots cooking (only add enough that onions float but carrots rest on bottom)
I would also add that roast the potatoes might be helpful. Also, you can alter the soup by pureeing some portion of the potatoes and adding it back to the pot.
In terms of a few additional ingredients: toasted sesame oil, fennel (whole, fresh), dill (whole, fresh)