>Mostly now that there is a lot of software that scales across cores better now

That's pretty much irrelevant since the AMD's FX arch's issues weren't that SW at the time wasn't using all the 8 cores. Intel dropped the Core 2 Duo and Quad into the era where most SW was still stuck in single threaded for a long time and those CPUs still ripped single-threaded SW tasks regardless.

Here's the big reasons why the FX sucked back then and why they still suck today in the multi-thread SW era:

  Instead of discrete, fully independent cores, AMD grouped processing units into "Modules" where each module contained two integer execution units, but they had to share critical resources like one FPU, the instruction fetch/decode pipeline, and the L2 cache so when both "cores" inside a module were heavily taxed especially with math or physics-heavy calculations (like in videogames), they choked fighting over shared hardware.

  AMD designed Bulldozer with a very long pipeline, betting they could sacrifice efficiency per clock cycle in exchange for extraordinarily high clock speeds(a-la Intel Pentium 4) but the IPC was so bad that an FX core was often slower clock-for-clock than AMD’s previous-generation Phenom II chips and also their power consumption exploded. 

  FX processors were plagued by high cache latencies and an inefficient memory subsystem as another bottleneck.

So yeah, modern multi-threading SW and kernels can't work around all those arch bottlenecks. Performance will still be shit. Like a budget Android phone from 2023 (Snapdragon 7s Gen 2) will absolutely destroy it while using 30x less power, that's how bad the situation is.

Last year I picked up an e-wasted FX PC for nostalgia tinkering and boy, it definitely feels veeery slow today(just like Core 2 Duo/Quad), even on lightweight modern Linux regardless of having as many cores as modern CPUs, the arch is just that bottlenecked, and when you add the missing modern instruction sets such as AVX2, FMA3 and SHA-NI, they only contribute to the slowness in modern use cases compared to today's CPUs that beat it while using much less power. It's fine as WindowsXP era PC for retro gaming I guess, but even then you can do much better with and Intel PC from the same era(i5-2500k for example) that's gonna be way less power hungry to boot. So unless you're into collecting pieces of history as display pieces, it definitely belongs in the e-waste pile instead of burning electricity.

How did AMD Ryzen get 50% faster in two years?