There is also a reasonably well sourced story that at some point during shooting of the Dalek/Father's Day block he remarked to RTD: "Why aren't all the scripts as good as this?" Which was a bit tactless as RTD had written all but one of the scripts he'd done up till then, and didn't help the atmosphere between them.
Harsh but very true. Wish Rob Shearman came back to write more episodes. I actually much prefer Jubilee to Dalek, great as Dalek is.
I'm going to hazard a guess that "Dalek" went through too many drafts -- Shearman went through at least nine. (It wasn't until the seventh that they took the Daleks out and replaced them with the Toclafane because it looked like the Nation estate wasn't going to play ball.) Too many drafts can sap a work of its spontaneity and its life.
And then Shearman's draft was rewritten by RTD, because RTD rewrote every script except for Moffat's.
So I'm going to say that "Dalek," while good, isn't as strong as "Jubilee" because it went through too many drafts.