Why is My High-End PC Underperforming?

I'm struggling with my PC build because it's not performing as expected, and it's really driving me crazy. I've thought about upgrading, but the improvement doesn't seem significant based on what I've seen. Here are my specs: I've got an i5 11400f CPU (I've undervolted it to -215 mv which helped the temps), paired with an RX 6900 XT GPU that's hitting 110°C during FurMark tests with a +15% power limit (it hovers around 105°C at 0%). I have 16GB of Adata XPG RAM at 3200MHz with XMP enabled, and my motherboard is an Asus Prime B460M-A. For power, I use a Gigabyte U1000D PSU, and I have a couple of storage drives including a 1TB Crucial P5 M.2. I'm running a fresh install of Windows 11. I've done all optimizations possible for Windows and BIOS but I still get below-average benchmarks. I can't figure out why my performance is lower compared to YouTube benchmarks, which is really frustrating. Additionally, is upgrading from an i3 10100 to an i5 11400f a mistake, or moving from an RX 5700 XT to an RX 6900 XT? I'm gaming at 1080p on a 165Hz monitor but considering moving to a 1440p monitor but doubt it will help. What's going wrong?