wait, what? 100 years? That can't be right.
It is. You only start out with +1 Dip rep, so you'd only be able to put 1 Dip point towards annexation per month. This forces you to get Diplomatic AND Influence to be anywhere decent at +5 Dip rep. Start a game at the Revolutionary France time (1792) and pick Russia. Add opinion to Kazakh and see that it would take 36 years to annex (for cheap lands) because you don't have anything to boost your Dip Rep. If you don't specifically take those 2 groups, you are SOL.
This slows the game down until you actually can fill out the 2 idea groups and forces even more expansion into the second half of the game. Of course, forcing countries to take specific idea groups for a major mechanic to be viable hurts those with fewer MP to spare (the ROTW) the most. There are NIs and advisors to go above +5, but not everyone has those NIs and the advisors need RNG to be available and at the level you can afford. There are a bunch of policies with +1 Dip rep, but having to further dish out MP over 10 years and be further pigeonholed into more specific groups is a bad design IMO.
I am really very surprised not to see more about this on the forums so far. It needs to be baseline +5 and ideas scaled down to +1, especially with the -3 malus whenever you finish annexing someone.
TLDR version of complaints:
1) Pigeon holes multiple idea groups for a major mechanic to be viable
2) Slows early game, forcing more expansion to second half
3) Pigeon holing groups hurts RotW as they will have fewer groups to use and are slower to fill