In all honesty, like others said you should think about it like two completely different products.
There are many reasons for this, from the ingredients, to the manufacturing process and the format.
Perhaps the biggest difference is the manufacturing and how it is stored. When you make the RTD, it needs to be in liquid state for the next 6 months + (whatever the shelf life is); avoid the precipitation of the ingredients; keep the smooth texture and still be edible.
In order to do so, you will appreciate that the ingredient list varies (to a degree that the macronutrient split is different):
- Oats are first for powder; pea protein and then tapioca starch is for RTD etc.
(I cover more of the differences in this huel rtd review).
So you have a different list of ingredients. That will affect the flavour.
Then you have industrial blending. Any RTD in the market will be smoother than the Powder counterpart; due to the fact that they are blended in companies specialised making these drinks. The blending process can take minutes or hours; in order to achieve an homogeneous texture.
The location, the water and the process this company uses can also change the flavour of the drink (as other brands have experienced).
All in all, you won’t be able to achieve the same drink with the powder, and I would recommend you instead trying to achieve something you like with it. Either via adding milk; more berries and blending; or going for a different flavour.