OP, you should not be offended. I've worked as an editor for a staff of eleven writers. I found that I had to be very careful in critiquing my writers because some of them took my comments personally.
Years later, I wrote books, which in turn were edited by professionals. In almost all cases, I had to admit that their editorial feedback improved the final product.
Even minor grammatical mistakes can become a mental speed bump to readers, jarring them away from thinking about your content and instead thinking about your grammar. When grammar mistakes are repeated often, as is the case in the OP's original post, the reader eventually becomes skeptical of the accuracy of the content as well. If the grammar is sloppy, how much trust can the reader put into the research done by the writer?
OP, let me critique your post to help you understand what I mean.
"First of all" [Delete this phase. We know it's first because you're writing it first. It's like starting a sentence with "So." It is not professional.]
Failure to precede the word "but" with a comma. [This is very basic grammar. Doing it twice in one paragraph makes it a real mental speed bump to your credibility. I find this particularly jarring, but it's fortunately an easy fix.]
Generally, you should avoid using "etc." in a sentence, although this wouldn't be considered a problem on message board.
"the SAT, have" This should be "the SAT and I have" or "the SAT, having." This is also jarring to the reader because it appears that you are writing a compound sentence with three or more parts, but there are only two.
The first sentence is 40 words long. This is more acceptable in scientific papers, but since the sentence is grammatically incorrect, the length makes it even harder to read. You should try to avoid sentences longer than 30 words, although this is sometimes hard to do in professional papers.
You should not be offended by my comments. I'm taking time out of my day to help you. My guess is that your advisor saw similar errors and wanted to help you get rid of them.