Will our engagement proves make our case strong or weak?

Your question requires an attorney consultation. It is not a simple question that can be answered on this type of forum. There are many factors that would need to be considered and evaluated. Your engagement in my opinion will make your petition stronger. I strongly suggest that you contact an experienced immigration attorney for a face-to-face consultation and give him/her all of the facts surrounding your situation. He/she would then be in a better position to analyze your case, advise you of your options and, if possible, make sure that the necessary paperwork and documentation is presented so as not to delay the process.

Both the petitioner and the beneficiary must submit a letter of intent as part of the initial petition for the fiance's visa.

I think the engagement helps your case. It shows your long relationship. And if you are married, then you should be able to come to the US as the wife of a US citizen with an approved I-130.

I think there is some confusion. Engaged to be married is not the same as being married. If your are legally married, then a fiance visa is the wrong visa. All couples who are engaged would seek the k-1 fiance visa. married couples seek the cr2 marriage visa.