It's interesting that in the first 90 seconds, he handily demolishes all the facile globe-earth arguments that you and your cohorts have already tried.
. So I'll give him that much. I'll listen to the rest later.
At the same time, Exalt wireless a couple years ago boasted of a record microwave transmission of over 100 miles across the Mediterranean. But ... microwave is known to be line of sight, which is why this record is so impressive (vs. radio waves which can travel thousands of miles). They forgot to do the curvature math that would have show this to be impossible on a globe (their towers were 50 feet high).
I haven't chimed in as a Ham yet, but although I'm Extra Class and very "into it" in many ways, the fact is that I can't spend that many hours on this hobby per week or per month, a lot of that time has been allocated to non-operating activities, and I've only been a Ham for 2 years.
Time spent building antennas, organizing my shack, building shelving, sorting through stuff, dissecting old stuff, watching videos about building radios, and dozens of other subjects don't add 1 iota to my experience *operating* ham radios. I actually spend very little time "operating". There are some hams like that, they're more into the technology and building things, solving problems, getting set up.
That having been said, I have heard a few things in my travels that would raise Flat Earth-inclined eyebrows.
1. References to mystery, or "I can't explain it" when it comes to direction and/or distance. "You just have to try it. I've had ______ happen and that shouldn't be possible, but it is. So just try it."
2. They do teach that line-of-sight VHF/UHF radio goes slightly "beyond line of sight" for some reason. I remember wondering why it curved with the earth just a bit but then stopped "for some reason" after some arbitrary distance. If VHF which normally is completely line-of-sight were able to propagate "ground wave", it should keep going, esp. if the ground is the right material (clay rather than sand) and you start with a high enough power level.
3. There are various atmospheric phenomena blamed for unusual or above-average propagation -- including 2 meters VHF. On a semi-regular basis, you can talk on 2M (with the right modes, and the right antennas) to different states -- sometimes several states away. These atmospheric phenomena include: Sporadic "E", tropospheric ducting, temperature inversions, etc.