I don't have EU: R yet but...
I think it's partially a problem of scale, and it applies to the entire EU series. It's just that in EU2 for instance, the AI is stupid enough to let the player grow. I.e. there's not much to do in the beginning as a minor, but you can fight off much larger AI armies due to its stupidity. Thus, you'll eventually be bigger and have more to do, and admire your new ahistorical major nation capable of beating any (AI).
It's probably realistic that Sparta would have an enormously hard time expanding at that point of history that you're describing. So far so good, assuming you're not playing Very Easy where AI should be a pushover.
But what if AI is smarter and doesn't let minors defeat it? Then you're stuck with a puny nation, where you have to wait decades to do anything. The scale of gameplay isn't developed for a one province minor. This is not something Paradox has tried to address. Their reasoning is probably like: "We design the game for the majors, screw the minors." I don't blaim them; the game would be more expensive to produce if they had to develop detail concepts for smaller nations (and abstract them away in larger nations to avoid micromanagement as nation grows).
The other side of the problem is regarding AI exterminating minors: There are very few reasons for minors to exist "naturally" in games of the EU series. It's just so easy to conquer minors and benefit from it, that killing minors off almost always is the best option. Hence no minors survive (at when the AI displays a minimum of aggressiveness). Leaving the minors alive would be suboptimal so I don't blaim the AI for playing as a human to present a greater challenge to big human controlled nations.
I think it's partially a problem of scale, and it applies to the entire EU series. It's just that in EU2 for instance, the AI is stupid enough to let the player grow. I.e. there's not much to do in the beginning as a minor, but you can fight off much larger AI armies due to its stupidity. Thus, you'll eventually be bigger and have more to do, and admire your new ahistorical major nation capable of beating any (AI).
It's probably realistic that Sparta would have an enormously hard time expanding at that point of history that you're describing. So far so good, assuming you're not playing Very Easy where AI should be a pushover.
But what if AI is smarter and doesn't let minors defeat it? Then you're stuck with a puny nation, where you have to wait decades to do anything. The scale of gameplay isn't developed for a one province minor. This is not something Paradox has tried to address. Their reasoning is probably like: "We design the game for the majors, screw the minors." I don't blaim them; the game would be more expensive to produce if they had to develop detail concepts for smaller nations (and abstract them away in larger nations to avoid micromanagement as nation grows).
The other side of the problem is regarding AI exterminating minors: There are very few reasons for minors to exist "naturally" in games of the EU series. It's just so easy to conquer minors and benefit from it, that killing minors off almost always is the best option. Hence no minors survive (at when the AI displays a minimum of aggressiveness). Leaving the minors alive would be suboptimal so I don't blaim the AI for playing as a human to present a greater challenge to big human controlled nations.