You haven't messed with Vcore or PBO during your time with the 3500X, have you? I assume you've tried resetting the CMOS jumper before pulling the CMOS battery?
It's supposed to be like that. POST concludes when the logo screen comes on, then you can access the BIOS. There's not supposed to be any video during that time.
You don't have to feel "scummy" for getting new RAM for testing purposes. I returned my Vengeance LPX because it was straight up shit and I wasn't going to put up with only using half of it at JEDEC speeds and being unstable at that. And if my first Trident Z kit (now my backup kit) didn't do the trick, I was going to go back and forth and try different kits until I got one that worked. I let the guy at the counter know exactly what I was doing, what I needed. You're a decent guy, you know how to handle electronics, you'll return the product exactly as it came to you so that it's ready for the next guy - as long as you're not damaging the sticks, they really don't care.
'tis the Ryzen life, trying RAM until you find one that works. Our atonement for being spoiled by Intel for a decade