With the caveat that I might be slightly out of touch (I have nothing beyond the Pi4/400 and the last x86 mini-box I bought was over a year ago)…

IMO the key benefit of a Pi over an x86/a64 box, assuming you aren't using the IO breakouts and such, is power efficiency (particularly at idle-ish). The benefits of the x86/a64 boxes is computing power and being all-in-one (my need was due to my Pi4-based router becoming the bottleneck when my home line was upgraded to ~Gbit, and I wanted something with 2+ built-in NICs rather than relying on USB so didn't even look into the Pi5). Both options beat other SBC based options due to software support, the x86/a64 machines because support is essentially baked in and the rPi by virtue of the Pi foundation and the wider community making great efforts to plug any holes. A Pi range used to win significantly on price (or at least price/performance) too, but that is not the case these days.