That's interesting... what do you mean by recent hardware? Some examples would be nice. What about an old AC68U v2 (B1) with dual-core 1 GHz Broadcom CPU?
Broadcom based routers are a no go as the WiFi isn't supported with the exception of the RT-AC88U, so I would only install OpenWrt on them for checking it out. My RT-AC87U, which has a similar processor to the RT-AC68U, does about 300 Mb/s max NAT, about what it did under Merlin with NAT acceleration turned off / QoS turned on.
To run OpenWrt it is important to choose the hardware that has the best support by open source drivers. Currently those are Mediatek and Qualcomm chipsets. A very popular router for OpenWrt recently has been the Belkin RT3200 / Linksys E8450 (it's the same device under two different brands), with the MediaTek ARM A53 MT7622BV (and fully supported AX WiFi), which can route 1 Gb/s without QoS, and it could be bought very cheaply a few months ago (around 50 GBP, even less in the US at Walmart) but now it has become hard to find. A similar device is the Netgear WAX206, which also has a 2.5 Gb/s port.
Also a possibility are devices based on the older Mediatek MT7621, which has hardware offloading support on OpenWrt and can route 1 Gb/s without QoS. For recent devices, these are popular mostly as AX WiFi access points, but people also use them as routers. Examples are the Belkin RT1800 / Linksys E7350 (same device) and the Netgear WAX202. I have two of the latter that I use as APs, I paid about 45 euros for them new on Amazon. They will last for ages, it's more likely that the hardware breaks before they're no longer supported as with 512 MB RAM and 128 MB flash (which are the main hard limits for a devce to become unsupported by a new OpenWt release) they have a long way to go.
The newer chipset from Mediatek, called Filogic, will be one of the best choices for OpenWrt AiO routers going forward, but it's still quite new and there aren't many devices with it on the market yet. Some examples are the Cudy WR3000, the TP-Link TL-XDR4288 and TL-XDR6088, the Xiaomi AX6000, the Banana Pi BPI-R3. There will be more in the coming months.
For Qualcomm, popular devices are based on the IPQ40xx chipset or the newer IPQ806x, but I don't know much about those other than they're popular with OpenWrt users, though not as much as Mediatek's.
For the best performance you can use an x86 (mini)PC, there's a lot of choice for those and also good deals on the used market. Raspberry Pi's are also popular with OpenWrt users. You can then add OpenWrt supported APs as per above.