I'm curious: What are you considering as a top CS school? At the one I went to, virtually no incoming student was a first author. Granted, this was a while ago, but it was still the case about 10 years ago.
2nd question: Did you actually apply, or did you merely ask around and get discouraged? My experience is that most of the advice people give on this topic is wildly off. That includes advice from professors in top schools.
Finally, GPA mattered in my time, and I'm sure it still does. It's not at all sufficient, but a poor GPA would almost always kill your chances. I those days, beneath 3.5 would be a guaranteed reject, and around 3.5 would be a weak candidate.
1) I'd consider MIT, CMU, Stanford, Berkeley as the top, as well as the top schools that aren't CS top schools but are still well regarded (Columbia CS PhD, Cornell CS PhD, Princeton, Harvard). University of Washington and UIUC among the top as well, as well as Georgia Tech, UMass Amherst, and UMD, though those are hardly of the same recognition outside of the field as the other ones that are well regarded.
2) I talked to a 7 (off the top of my head) professors at a few institutions about this as well as a 5 PhD students, one from my undergrad (people from my undergrad don't generally go to top schools for PhDs in CS). All of their profiles had multiple first author papers and none of them got into any other top school than the one they went to. Ofc, the ones that went to top undergrads did get into multiple. The circles your professors runs around in at state schools absolutely matter. Mine is very well regarded in the research niche but that doesn't transfer well to even adjacent research niches.
I got a 3.92 at my undergrad, CS GPA around 3.98 or so.
I went to GaTech, picked a random PhD student and looked at his CV. He had only one paper prior to starting at GaTech, and he was the last author. Picked another one and that one did have a first author paper. Couldn't find CVs for the others I picked.
Went to UIUC. First random student I picked had no publications prior to joining UIUC. 2nd one I picked had one, but not as first author. 3rd one I picked had none prior to joining UIUC.
No particular subdiscipline. I just now picked a random MIT EECS grad student who went to a state school of equivalent ranking to mine (rest went to top schools or MIT itself) - he had 2 first author and 1 book chapter as well as a workshop (also first author).
I do want to emphasize that the people that go from Undergrad to PHD at the same school does skew the profiles a bit, especially if they already researched with the same professor.
What field are you in? Most engineering programs will not require this.