I’m going to take a counter point out this and say that I think that R2 D2 unit can defeat a Dalek.
So some of you may be asking how?
Well just like the Doctor, R2 D2 is a very intelligent and adaptable. It is true that he has no real offensive weapon capability beyond being able to shock, but neither does The Doctor. If the Doctor can defeat the Daleks without using heavy weaponry, then so can R2 D2.
R2 D2 can get an edge over the Daleks because simply put, Dalek’s have shown that they lack the ability to learn and adapt. As such, I can see R2D2 setting up a trap by tricking the Dalek into going some place where R2 D2 can manipulate it and trap the Dalek into a defeating situation.
Plus unlike the Dalek’s, R2 D2 has very powerful friends. If he really wanted to, R2D2 can also get a signal and alert the Rebel Alliance so as to call in an squadron of X-Wings and A-Wings to take out any Dalek’s that cause trouble. As for the Daleks, they have no friends because no one really likes them.