I have a BDB and can tell you what I have found gives me the best flavour. Given taste is pretty subjective, it may or may not be what you are looking for but it seems to give me balanced shots with good amounts of sweetness, acidity and bitterness.
In my experience, based on lots of trial and error and also using the razor tool as a guide to optimum dose for the Breville basket, I have found that it works best with 21g. In your bottom video it looks like it is running too fast and channeling round the sides of the puck. It's likely this is just due to their being too little coffee in the basket and should resolve when increasing the dose to 21g.
Usually I prefer a 6second pre-infusion, then ramping up to full pressure. If it tastes bland or sour to you it is likely you are either under dosing or under extracting, or both. See how it tastes when you increase the dose to 21g in, with 42g our in around 30 seconds. You may want to then try getting the same yield in 25, 30 and 35 seconds (by altering your grind) to find which tastes best to you.