The phrase "technically speaking" is correct and usable in written English. It is used to emphasize a point that is based on a specific technical or scientific fact. For example: "Technically speaking, the human body is composed of 70% water."
Technically speaking, sure.
Well, technically speaking anyway.
Actually, technically speaking, that's not true.
And, technically speaking, this was true.
Technically speaking, it wasn't theft.
"Technically speaking, he's an auteur.
Technically speaking, Lugo was impressed.
Technically speaking, this team has the edge".
H.P.P.D. does not generate hallucinations, technically speaking.
Technically speaking, that slice was an impossibility.
Technically speaking, the stock has put in a rough performance.
Being a terminologist, I care about word choice. Ludwig simply helps me pick the best words for any translation. Five stars!
Maria Pia Montoro
Terminologist and Q/A Analyst @ Translation Centre for the Bodies of the European Union