I find it very difficult to place merit in such a decision.
That's okay, there's a 28+ thread on the topic where others (including the developers) also found it difficult to place merit in the decision. All we got was something along the lines of this "argument":
Same continent colonization gave you full provinces for very little cost. It was very strong.
Of course, demonstrating no quantitative analysis as to how the investment in exploration compared against alternative idea groups absent the westernization factor, no true comparison in the cost of colonies fronted or the opportunity cost, and no demonstration of nations that actually suffer the nerf (Americas, Africa, Siberia) actually needing the nerf. Meanwhile, the strongest nations in the game get more tax for their CNs because by the same "obvious" logic, overseas expansion didn't need to be nerfed.
None of those ideas, unfortunately, are better than the current system. Having to 'core' dozens upon dozens of new colonies, which will turn into Colonial Nations or Trade Companies, would make the system even less lucrative. Colonization is a more peaceful way of expanding your nation. It should not be of equal value as taking a fully developed province through conquest.
Your statement is not consistent with a need for a 50% LA floor. You could start colonies with 75% autonomy and leave them as normal for example, and colonization with the up-front costs and delay would take a long time to become useful, nowhere near what you could possibly do with alternative means of expansion.
This is, of course, ignoring the reality that conquest as anything other than a native (which runs out of targets) can gather base tax and value much faster than colonies possibly can do so.