Improve the AB Split functionality to ensure the segment splits to the proportions set in the customer journey design. For example, you can select 50/50 split but it won't split 50/50 - it could be 30/70 or any random ratio depending on how the journey and segments compute etc. If the segment is too small, enhance functionality to embed a minimum test size.

This is a major functionality gap between many off the shelf email marketing software platforms.