I don't know about the dev's idea but I think any path can be main path.
For example, I prefer Lucy as you know.
I can say, her path is the main path for MC because Lucy is the one who holds the Lloyd family together. Whenever Suzi or Emma needs an advice, they seek Lucy's. Many times Charlotte mentioned she is her rock too. Also, except Lucy all the Lloyds needed MC's help. So in a way, MC meant to stand together with Lucy to protect Lloyds. Their fates tied together. Lucy only opens up to MC and MC only opens up to Lucy. MC does not have such a relation with any other Lloyd, though I admit it's too soon for some.
Have you played Lucy's path? Can you compare it to Charlotte's? If you try both, in Charlotte's path MC always talk about how perfect a woman Charlotte is, how good looking she is etc. but he does not talk about his own place in the relationship. On the contrary, in Lucy's path he always talk or think about how Lucy always felt meant to be.
All in all, I am not gonna claim any path as the main one because I know it's not true. That's the beauty of this game anyway. Whomever you choose you feel you chose the right one.
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Solely this scene is enough for me to not waiver on Lucy's path.