truth about sorority rush

No, those things aren't really true. Let's take it one at a time.
Insta - Sororities don't really care about your followers unless you have a really tiny amount or a staggeringly large one. Otherwise, it's just another way for them to see a little bit about you along with your video, resume, and GPA.
Larger PC - The more pnm's the more bids. There is not a preset number of bids and the process is not designed to get rid of pnm's, it's designed to place as many as possible in sororities and maintain equity among the chapters. Everything is percentage based, not on hard numbers, so you have the same chance no matter how large or small rush is.
Knowing people - While it is always an advantage to already know active members in a sorority, it is not a disadvantage if you don't. Tons of girls have a great rush coming in knowing no one. Recommendations are the same way, they are an advantage if you have them but not a disadvantage if you don't.
The things that matter for the first round are your GPA, your resume, your insta, and your video. For philanthropy and sisterhood rounds it's all about how you present yourself in person. You need to look good and have good conversations. Sororities are looking for their sisters, so making connections with the actives you meet and enjoying your time talking with them are key. Be confident, positive, and interested. They want to see your personality so show them your best authentic self. Girls who try to fake who they are always have a bad rush. And if you have a favorite house at sisterhood, you need to tell them how you feel.
Hope this helps, best of luck.