Do I even need to use Experiment Designs, what’s wrong with randomised treatments?
You don’t need to use designs - but then there’s no guarantee the data can be modelled.
Without a directed, fit-for-purpose design one has no control over learning effects and dominance.
An appropriate design controls for these and gives you statistical confidence that you can capture the necessary variation for valid models. For small or limited samples an experiment design is critical to success.