Not sure about that. The 3900X is 200 W full system, 10900 is 240 W, so your argument becomes "$100 boards can handle 200 W, but not 240 W" ? Could be a possibility, not convinced, but I don't have any good data.
Edit: Did a quick test just for you, 10900K @ 5 GHz manual, Prime95 = 225 W. 10900K because I was too lazy to uninstall the 10900 from the ASUS board
MSI Z490 Gaming Plus (which I bought for € 155 in retail), VRMs just warm, plenty of headroom, cooling the CPU is almost impossible though, with that Intel TS cooler
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