I think the difference between OpenWRT and pfSense is that pfSense only runs on PC class hardware, while the kind of device that usually runs OpenWRT is far less powerful.

I used to run OpenWrt on my router ... years ago, and I remember that router had 16 MiB RAM, and a 125 MHz MIPS CPU. If you set up such a machine, say, as an OpenVPN server, this would seriously limit the amount of data I could push through the VPN connection. (Not really, because my Internet connection is not very fast, but that is beside the point.)

Even a Raspberry Pi is far more powerful than the typical OpenWrt router (at least the ones I have handled).

At work, we set up a wifi network using OpenWrt routers, using separate wifi networks as well as different VLANs for employees and guests. To get a vendor-supported solution that can do this, you have to have spend a lot of money.[1]

So in my experience, OpenWrt is a lot better than what most commodity routers/wifi-access points offer. With the exception, maybe, of the Fritz!Box family.

[1] Okay, it depends on your definition of "a lot". In our case, the requirement was to make it as cheap as possible, because strictly speaking we had no budget at all for the wifi.