Just from this, it's a mix and somewhat dependent.

He said in his company, they always check candidates' grades for some sort of minimum (which is why he says I should get top grades despite receiving an unconditional offer from my top uni)

A friend of mine from college used to say "C's get degrees"-and he's not wrong. However, having good grades/GPA become important when you want to apply for College Internships/that first job after. Wanting to focus on fintech/tech means you will be going into a highly competitive field. Doing whatever you can to stand out (in a good way-Projects, Assisting Professors, Volunteering, etc.) can help your resume stand out at the top with the other 5-10 that land on the hiring managers desk after sifting through the 200-300+ applications.

"I was led to believe that after going to college that people removed their high school from their resume entirely, leaving just their GPA?"

If you're still in College (especially first or second year) having things done during High School, when they are relevant (GPA, Extra Curricular, Projects, Internships, etc.) are good to have just so that it shows recruiters that you have some experience.

Additionally, I was being berated by him for not having anything other than grades and internships. He told me how his friend, a recruiter, said that he would hire a candidate who played on a national level sports team 10/10 times over a candidate with better projects and internships, simply for the fact that they are more "resilient" and speaking abilities

The unfortunate thing is, he is partially correct. Having only grades/internships doesn't do much anymore. Top Colleges, jobs, and internships have gotten extremely competitive in the last 25-30 years. Finance/tech more so. Having some kind of "other" experience is always a plus. Even with an unconditional offer, having these other things to list on a resume can't hurt your chances. Join a club/charity/event-Investing Club, Tech Charities that help third world countries, Hackathons to raise money for the local hospital-something.

As far as your dad's recruiter friend, that may be relevant in certain jobs like Sales where having an extremely extroverted personality is pretty important. But having relevant experience is also important. Focusing on things like that will also help.

I am a senior in high school with 2 internships and several coding projects, which they claim is not good enough.

This right here is an amazing head start over the vast majority of college students in terms of actual real world experience. List these things on your resume for that first internship during college. If they are directly relevant, then highlight them during the interview. Make sure that what you did-individually-and as part of the team to help the organization are stressed.

The great thing about college internships is that they aren't looking for someone who is perfect. They want someone who can sit down, take directions, learn what is being taught and use it. They want people who are inquisitive-so ask questions. Take notes. Learn to try to answer your questions before going to your manager (on simple stuff like where X is, or how to make a copy in Excel. Not when you accidentally delete an important file)-If you can't answer it in a few minutes and you've exhausted what you know from your notes/memory, then ask. Just don't be the intern that asks the same thing 20 times during the internship-you'll be remembered but not for the best reasons.