I'm not sure what you're talking about. Any app compiled using LLVM 17 (2023) can use SME directly and any app that uses Apple's Accelerate framework automatically takes advantage of SME since iOS 18/macOS 15 last year.
Benchmarking a processor for "app written by someone who disregards performance" is something you can do, but it's a bit of a pointless exercise; no processor will ever keep up with developers ability to write slow code.
Of course. And these are CPU vector instructions, so the saying "The wider the SIMD, the narrower the audience" applies.
But ultimately with a benchmark like Geekbench, you're trusting them to pick a weighting. Geekbench 6 is not any different in that regard to Geekbench 5 – it's not going to directly reflect every app you run.
I was really just pointing out that the idea that "no" apps use SME is wrong and therefore including it does not invalidate anything – it very well could speed up your apps, depending on what you use.