Is that a shock since the BoP is like 80 years old while the Defiant is still on the run out stage of a ships life.
Perfectly true. That is, however, what the OP asked. If someone asked 'What's the better plane, the P-51 or the F-22?', then I think I can guess the right answer.
Bear in mind also that whilst small 12 person designs are 80+ years old, there are also newer, larger designs. The Defiant seemed to do well against them during the Klingon war.
I fully agree that in missions where stealth is paramount the BoP has the edge. But I'd prefer a Defiant for a pure combat mission.