If only we hadn't fought Hitler the German army probably would have just given up, turned their guns into ploughshares and planted pretty pretty flowers everywhere...
I agree with this. The Doctor *had*
to fight the Daleks because they were already evil. It's possible that by defeating the Daleks at various points that they were motivated to improve their game. However, without the Doctor, the Daleks would've been able to conquer more despite being less motivated/skilled. And, after the Doctor's interventions, they may have been a bit more motivated/skilled, but they conquered less.
But, make no mistake. The Daleks were always evil and were always intent on enslaving and exterminating all other lifeforms.
Having said that, I can see how given the situation in the modern Whoniverse, the Daleks, as they currently are, might rest on their laurels if they are unaware of the Doctor. If that's the angle Moffatt is taking, that's fine. No point stirring up a beehive if you don't have to.
But, to suggest that the Doctor shouldn't have intervened before is just preposterous!