Dominant soil formation process

yes, that is correct - in Podzols there could be 2 dominant soil formation processes - accumulation of Fe/Al oxides/hidroxides (indicated as Bf) and accumulation of organic matter in B horizon (indicated by Bh). Some (but not all) Podzols will have either both of those processes (indicated by Bhf) or just one of those 2 processes.

In general, assigning the specific dominant soil forming processes to each of 10 soil order is based on the current, overall understanding of soil formation (genesis).
However, if you are asking how is an individual soil scientist or land manager deciding what is a dominant soil forming process in a specific soil, than the answer is - based on field observation and description and (if necessary) lab soil analysis.