That's actually a neat thing about our new DLC model: Back when HoI3 came out Paradox could only budget for 3 patches per release, because you have to be making something you can earn money from to stay in business. HoI3 actually got a 4th patch just because it really needed it, above the budgeted 3. After that, it could not be worked on more unless there was a salable product attached, like Semper Fi, and then only people who bought SF got the benefit of the work put into it. That's all changed now, for newer games like CK2/EU4/HoI4 we can continue working on the base game for its budgeted patching time, plus as long as people are buying DLC - it's all one game rather than a set of discrete versions.
Still, again, we want it to be good on release and now to have longer development time and proper QA to help that happen.