A student with IGCSEs result

Hey all,

I am a non-US student, who was attending an international school in the Singapore.
Here, students follow the a 2-year IGCSE curriculum developed by the Cambridge Exam Board.

Here is my situation:

I want to apply to the university in the US, after taken the final IGCSE exam last year in June I didn’t take part in any academics study due to some reasons. Currently I am only holding IGCSE and IELTS results (no SAT).
MY QUESTION IS:
I know there are some universities in the US can accept with only IGCSEs,but Is it can be consider as a high school diploma?
And If I did got into an university with this degree will I have trouble when I want to transfer to an better university even I had gained enough GPA?
Also I had visited some agents here they all suggested that I should take a pathway course provided by minority universities(one year special program offers to international students who needs help in English you will become a sophomore directly when the courseis finished)
Do any of you know this kind of programs well?what’s the advantages&disadvantages of it?

Thank you for reading I will really appreciate your help.