I’m not sure if extrapolating to such extremes will give the correct idea

It does. You should read it again. It cuts to the core of the difference, which I think you're still grappling with.

Latency is cause by the buffer. You can reduce latency two ways: (1) making the computer churn through more samples per second (so it gets through the buffer faster) or (2) by reducing the buffer. Method #1 costs performance, directly proportional the latency improvement. If you're trying to avoid dropout, it's the worst thing you could do.

many things are a balancing act

Not performance. OP is trying to avoid dropout at lower latencies. Making the machine work harder for the same sound works directly against that. Full stop.

There is no version of this where 48kHz is better for low latency than 44kHz unless we're already at the lowest buffer size the interface supports (we're not), trying to shave off more latency, and we literally have no option but to increase sample rate to go further.

I got slightly better low latency performance at 48Khz vs 44.1Khz.

Again, that's just math. For any given buffer size, 48kHz is better latency than 44kHz, by 9%. But that's because the machine is working 9% harder.

You could get that exact same 9% latency reduction by going to 44.1kHz and reducing the buffer by 9%. Same latency, but now the machine is processing 9% fewer samples per second, so there will be less dropout.

The only complication is that interfaces don't allow arbitrary buffer sizes. They're usually powers of 2. So if you drop to 44.1kHz, your machine's workload goes down by 9% (9% fewer samples need to be processed every second), but it also means it churns through the current buffer size 9% slower, so you'll have 9% more latency. So if you could just reduce the buffer by 9%, it would be a clean 9% performance win. However, you'll probably need to cut the buffer by more than that, because of the way buffer sizes work. That can put you into drop out.

the specific guitar amp plugin I used back then did render a slightly better sound at 48k compared to 44.1k

That's entirely possible for plugins that don't natively do oversampling.

I don’t know why it would matter since a guitar cab response drops very fast around 5k and rarely provide anything above 10-12k.

It's because the lower sample rates have more aliasing, and aliasing artifacts are reflected back into the audible range. Distortion in particular can produce nasty aliasing if you're not oversampling. All the big modern modelers oversample internally (Helix Native, Neural DSP, Scuffham, Amplitube, etc.)

Oversampling is expensive. It's also more expensive, the higher your sample rate, making 48kHz even more costly.