All of these tasks are "accelerated" by skimping on quality or using silicon dedicated to a specific program. It doesn't matter in real life unless literally the only thing you do is use a browser and nothing else, and even then only JS, not wasm. In which case, I don't know why you would even have a CPU with more than two cores, and an i3 would be more than enough anyways. JS acceleration really only matters if you want to maximize battery life and the only thing you're doing with your computer is contained in a traditional webview. That is to say, it matters little for laptops, as they already have 7-8 hour battery life, and literally not at all for desktops.
So, for example, my computer can encode 4 4K videos in real time simultaneously. Why don't I use this feature? Because the encode quality is subpar. So unless you give me a benchmark of the iPad Pro on ffmpeg or any other open source, non-hardware accelerated video encode software, comparison is completely moot. And the benchmarks that have been done on ffmpeg on x265 or x264 show that the iPad Pro is multiple times slower than an Intel laptop. Now obviously x265 is optimized for x86, but not on the order of multiple times slower. Unless it is the case, and that means that your benchmarks don't apply either.
Herein lies the issue, for many many workloads hardware acceleration while faster offers results that are not comparable to the CPU in terms of quality. So the only way to compare is by disabling hardware acceleration, and x86 processors tend to win.
Metal is a trash API that no one uses in the real world. It offers literally nothing better than Vulkan. And the fact that the chip is "customized for the API" is vacuous. All GPUs are optimized for OpenGL, DirectX or Vulkan. Same for a lot of the "Core" APIs. They will not succeed outside of the mobile market.
The T2 chip is simply a glorified security processor. There is absolutely nothing the T2 chip does that a traditional security processor in say a Zen chip can't do. x86 CPUs can already do AES at speeds so high you would need something like 4 RAID-0 NVMe SSDs to have a performance bottleneck, and even then the limitation isn't the CPU but RAM speed. There is no real world scenario where you would need to "accelerate" disk encryption or other kinds of cryptography beyond what an x86 CPU can do. Cryptography isn't some kind of magic you can't implement without some specialized chip, literally everything the T2 chip does can be done using a trusty old x86 processor and TPM. The only use of the T2 chip is for Apple to have more control over your hardware, and literally nothing else.