OK let's start playing Portugal and colonize!
50 years in; woops, turns out you need The Cossacks DLC to set your attitude towards natives. Have fun stationing your troops all across the world and paying permanent maintenance for your entire army to prevent native attacks. Also, i guess you cant afford to attack northern africa or expand cause half of your army will be guarding your colonies overseas for atleast the first 100 years.Cause you bought only conquest of paradise and mare nostrum for your colonizing game. But set native attitude is (logically) in the steppe peoples and estates DLC.
You actually get an event to set your policy once you started your first colony (MTTH: 1Month). And at least all the colony events are tied to your choice there and I blieve uprising, etc aswell.
So yes, there are cases where the paid features are poorly accessible when you don't have the dlc, but for others there are mechanics provided for non dlc owners.
Also the thing everyone forgets is: if you can't develop, so can't the ai.
What does this mean: The neighbouring AI, which is most important, has neither development nor institution advantage over you. And in most cases it is just fine to let institutions spawn naturally or conquer provinces which have the institution embraced. Which makes no difference between dlc and non dlc.
If you just look at institution development you on average have to spend 2000 points on it. in order to recuperate that you need to tech up 6.6 times if you are behind 50 years. so yes it may make a difference to european nations. but NOT to your neighbours. and if you embrace an institution it spreads to your neighbours as well. So technological it makes no difference, whether you have it or not.
The only difference is the worth of the province. But when you own the dlc and develop provinces so does the ai, which leads to the difference:
With DLC: You have more money, tech, ... As do your neighbours
Without DLC: Less money, Less tech, ... As do your neighbours.
And this is something often forgotten...
Yes I agree that DLCs need a restructuring of sorts and adding older DLC as part of a bundle would be nice for new players. But making everything older then 1 year or so free or adding the mechanics to the base game is totally over the top. And definitely not a wise business decision even if you get more exposure that way. Because then you let people also get accustomed to the mentality: "If I wait 1 year it's free anyway."
And if you play MP the DLC of the hoster are available to everyone, so no need to argue with that either.
And if you are whining about dlc prices you have to factor in the following:
Every patch provides free content and paid content. The thing is, the free content is not actually free in terms of development costs. So when you buy the dlc you are also paying for the free content, notz only the paid content. But that is where you have the choice: Do I buy the dlc or not . Compared to other games you have the valid choice of not buying a dlc and still getting nearly as much out of the game. Which is actually really customer friendly.
TL;DR: Yes restructuring of DLC would be good. But making the DLC content entirely free not.
Edit: And honestly a lot of stuff in the DLC would confuse new players even more in a complex game such as EU4. So it provides the option to learn a bit and then, if you like the game, get a dlc or two.
Also: if you just calculate how much you pay per hour played it is at least way less then a lot of other games. You pay probably around 10-20€ per DLC. Even cheaper on sales. If you play 2 games or so per dlc, which allows you to experience unique things about the dlcs without getting too much repetitiveness, you still play around 30- 50 hours or so, which results in around 0.5€ per hour. Which is quite cheap for games if you just look around a lot of new titles.