Are wired IEMs really better than true wireless earbuds for sound quality?

At equivalent prices, yes, and it isn't close. Wired IEMs skip the DAC, amp, battery, and Bluetooth codec compromises that wireless earbuds have to package into each earpiece, so more of the budget goes to drivers and tuning. The trade-off is no ANC, no on-ear controls beyond an inline remote, and you need a 3.5mm jack or a USB-C/Lightning dongle.