Oxford Advanced Learner Dictionary says that the idiom so to speak is used to emphasize that you are expressing something in an unusual or humorous way
E.g.
They were all very similar. All cut from the same cloth, so to speak.
I was told by a native speaker that so to speak is similar to the phrase let's say when I was asking how to use this phrase. Then I tried to confirm my understanding by asking whether it's also equivalent with suppose/supposing. Then they said yes. If that so, then, is it also equivalent with Imagine that and Consider?
I'm more confused, honestly. The definition from OALD above clearly states it's used to emphasize something unusual or humorous. And the answerer made me think that this phrase is used to imagine that is something is true or make an assumption. Is it how exactly they use this phrase? Or I've misunderstood?