As a law student who decided law wasnt for me, this is false. The issue is that there is a forced curve and come finals everyone knows the law well, its all about who can write an exam answer in the format law professors like, and they all have different preferences. That is why many people feel that grading in law school is arbitrary. The old adage is that you dont take contracts, you take contracts with professor x.
Paralegal experience has virtually no impact on grades outside of maybe legal research and writing, which is usually pass fail anyway at top schools.
As for the OP I cant tell you what to do but I can give you advice is you go to law school. I went to a lower ranked school with a full tuition scholarship because I was afraid of debt. DONT DO THAT. Go to the best school you get into. PAYE makes most of that debt irrelevant if you dont get biglaw. But where you go to school WILL follow you around forever unless you decide to go solo or start a small firm.
If you are being graded on a curve or against other students, then IMO it really matters whether they are A-students, C-students, etc. And it matters if your competition tends to be prepared and plan ahead. I would much rather compete against a group of F-students.
Paralegal experience is a much needed boost. Gradewise, it will help the most in legal research and writing, but will set you apart from your non-paralegal peers in many ways. Having paralegal experience will get you hired easier and will help you move up the ranks. (It's not the only factor. It will help.) A paralegal certificate is also easy to get, costs only a few thousand dollars, takes less than 6 months, and paralegal positions are easy to find. There's no good reason not to do it. Employers love paralegal experience.
You don't need to go to a top school to get into BigLaw at all. But, like medical school, you do need to make yourself impressive somehow. If you pursue BigLaw with the same amount of time and energy you would put into medical school, there's no reason for it not to happen. If you are really stuck on BigLaw, make your 1st year grades rock, and do everything I said above. Most people don't. Most people who apply to law school don't qualify for medical school. You can't compare yourself to them in this situation.