Less 'aggressive' phrasing/word for "ruthlessly remove unnecessary complexity" from requirements

Cull complexity (for the ruthless connotations)

Trim the requirements.

Decimate complexity (also ruthless, but in the literal sense only paring down to 9/10, so maybe not as far reaching as you'd like)

Skeletonize the requirements (i.e. reducing them to bare bones..., also image processing lingo with appropriate connotations)

Thin the requirements

Erode the requirements (only applicable if you exclusively communicate with people who are into image processing, otherwise the meaning is lost or even reversed)

Axiomate the requirements (invented word, referencing axioms as the irreducible foundations of something)

Distill the requirements (by getting rid of all the diluting fluff)

Crack the requirements (only for specific audience; https://en.wikipedia.org/wiki/Cracking_(chemistry))

Condense the requirements (Changing them from the hot-air-like gaseous phase to something much less voluminous...)

We used to call it pruning in my day as a software engineer

Prune : to reduce something by removing things that are not necessary. Cambridge Dictionary

leanify is not recognised as an English word by the same dictionary, although it is used as a name for one or more pieces of software and a number of fitness training companies!