Once you understand and have mastered all the systems of the game, what exactly is there to do except expand?
I know you don't have an answer, because expansion is the only consistent goal in the game, regardless of whether you start small and attempt to survive (which almost always requires growth) or start large. Trade is shallow, colonization is just another form of expansion, diplomacy is meaningless unless it is used for expansion or to prevent enemy expansion. If you're not expanding, then all you're doing is watching the clock tick down and playing choose your own adventure with random events, which is certainly not the reason any of us play grand strategy games.
If you're not expanding, you're not actually playing the game, and if you're not playing the game, what in the hell did we buy it for? When you can point out a strategic challenge in the game that doesn't revolve around expansion, maybe we can talk about how blobbing isn't supposed to be how the game is played, but for now, expansion and border growth is the only way to make the game challenging, and the current systems transform it from a challenge into either a spreadsheet management game of AE values or a rotating coalition slog, with event roulette bolted on the side.
Rather presumptuous cause in fact I do have an answer.
To use France as an example my playstyle is set within a historical frame. My goals by 1820 are the Netherlands, the left bank of the Rhine, parts of Italy (Milan or the Anjouan heritage), a colonisation effort in N-America (preferably Canada and parts of the 13 colonies), islands in the Caribbean, a strong position in India and Indonesia and in between strongpoints along the other coasts in Africa, Asia, etc but never large swaps of land.
If I'm Castile my goal by 1820 is form Spain, strive towards the recreation of the empire of Charles V or Philip II, have strongpoints in northern Africa (Presidios as they are known in history), beat the Ottomans at sea with a gigantic galleyfleet, colonise Middle and Southern America, Brazil if I can beat Portugal to it, establish myself in India, Indonesia and the Philippines.
If I'm Japan (or a Daimyo) my goal by 1820 is to unite the islands, colonise towards SE Asia, conquer Korea, Manchuria and parts of coastal China and SE Asia.
If I'm the Ottomans my goal by 1820 is the Balkan, Egypt, N-Africa through alliances, the Arabian peninsula, the Caucasian and Mesopotamia, I'll challenge everyone in the Mediterannean with a massive galley fleet, keep Russia, Austria and my Persian neighbours in check, strive for naval dominance in the Indian Ocean as well. Shit and Malta, I want Malta.
If I'm Venice. I don't play Venice cause I can't set a goal hahaha
I specifically preserve my foes like England and I'll allow them to colonise parts of the world if only to add to the challenge and to be able to wage global wars in Europe and the colonies.
I can go on and on. I'm enjoying it enormously so far. I'm playing the game as I'm not expanding for I'm planning my next move, colonising, replenishing my revenue, building, cementing alliances, preparing fleets and armies, etc. I sort of roleplay a historical setting you might say, but I don't recreate history to the date to the very province cause that would be silly. That's what I bought it for.
Not WC.