So, I specifically said that SSE was better for the vector arithmetic that games do. Almost any game you pick will, in the source somewhere, have Vector3::Add(), Vector4::Dot(), etc. functions.
Scalar code is not trivially fixed by using SSE, true, but the majority of really obnoxious math being done (skinning, vector arithmetic, etc.) should be really easy to make really fast.
Right, which is missing the point. The use case at hand is rebuilding some particular part of the engine (honestly it's unclear to me exactly what was done) with different flags, not reworking the vector librar{y,ies} to use SSE.
SSE wouldn't be a flags issue. Building a vectorized SSE library in "debug mode" would still produce vector instructions.
Scalar code is not trivially fixed by using SSE, true, but the majority of really obnoxious math being done (skinning, vector arithmetic, etc.) should be really easy to make really fast.