I feel there's a 3rd, much more obvious (and in my mind, likely) possibility - they're simply not as fast as x86.
x86 vs ARM is not a new thing, it's something that has been debated for years and years. They're ultimately both very good at different things but apples to apples, ARM is way more efficient at lower power draw and x86 is way more powerful (And expensive!) at higher power draws.
We've seen both sides of this - we've seen x86 in embedded devices,
like phones and got great performance with awful battery life. We've also now got
ARM in the server space, which (shock horror) isn't quite as fast as its x86 counterparts but works out much cheaper overall as they're cheaper to run (And presumably cheaper to buy). Keep in mind those benchmarks were against slightly older-gen x86, but even then it's clear where ARM shines and where it doesn't.
I would not expect to see performance gains here at all, that's not what ARM has ever been about , but..comparable performance is still nothing to be sniffed at.
Apple tends to have some pretty awful thermal designs in their machines, so you might even see better performance just from sheer efficiency, but Apple aren't going to be looking to knock Intel or AMD's performance crown off any time soon.
Keep expectations in check, competition is always a good thing.