This is for sure not the case! The country's different economic systems enable and prohibit both certain pop behaviors and actions the player can take, in addition to making it easier or harder to engage in certain playstyles. So both a set of hard locks/unlocks on actions and modifiers/cost adjustments. We'll get into more details on this in the near future.
Like @Wizzington has hinted at a few times already in this thread, a crucial bit of design intent behind our approach to never prohibit the player from engaging in new construction, or put construction wholly on AI autoplay, is that
choosing which aspects of your country to invest into and expand - represented by different buildings - is the core of Victoria 3, informed both by economic and political concerns. Expanding an Iron Mine in a newly conquered unincorporated part of your country can have very different long-term knock-on effects from expanding one in your capital, and predicting or discovering these kinds of effects in retrospect is a big aspect of our enjoyment when playing. We don't want the player's choice of economic system to either make the game unplayable because of micromanagement requirements nor remove the society-building aspect from the experience.
To put this a different way, we want the decision to switch to a different economic system to be based on a play strategy that develops in response to the game. For example, the Industrialists (or the United States) might demand you open your market and you decide you're not in a good position to fight them, or perhaps you welcome the opportunity. This demands each system be a valid choice in its own right, without forcing the player into a kind of game they don't like playing. We never want to force the player to make a decision about which direction to take their country because the alternative is boring or impossible to manage.
But that for sure doesn't mean it should feel the same to play a Laissez-Faire country as one with a Command Economy.