Overall, GPU strength is the best it's ever been in portable Apple devices by a significant margin. The problem isn't the hardware, it's that game developers are reticent to support anything that's not x86 Windows+DirectX or one of the consoles.
It's often said that macOS/iOS supporting Vulkan would help and while I think that's true to an extent, native Vulkan support is still rare enough that it's not going to change all that much in terms of ease of porting. It might improve things on the front of running games through WINE (DirectX → Vulkan translation), but unless developers produce ARM builds of their games there's always going to be the overhead of being run through an x86 translator, which varies depending on how CPU heavy the game is.
Anything other than metal will be a big win. It's just a non-starter for developers of desktop quality games. Mobile ports sure.
But Apple has never really cared about gaming. During the powerpc era they had a short phase of paying aspyr to make some ports (most notably CoD 4 modern warfare and some battlefield ports) but it was over within a year.
Then about a decade later they had a phase around the 320M chipset where they promoted game releases. And again within a year they dropped the efforts and also let their OpenGL go totally stagnant. This caused for example elite dangerous to drop support.
Now we're stuck with metal. Apple is just too small in gaming for desktop game devs to bother with metal. Not sure if Vulkan will be best but metal surely isn't. And the added complexity of building for arm doesn't help either (arm on windows is non-existent on any hardware aimed at gaming)
I don't think Apple and Mac gaming will ever really become serious. I'm sure that if they do partner with studios like the last few times they'll just abandon the efforts like they always have.
I think the biggest problem is just Apple's total lack of interest (save for the few half-hearted efforts above) to make Mac gaming real.
I think a bit in the first sentence in your first post is key.
They don't want devs to think as Macs and iDevices as separate targets, but rather as one big platform. They don't Mac ports, they want Apple platform ports.
It makes some amount of sense. App Store revenue split aside, iDevices massively outnumber Macs and the gap in graphics horsepower between Macs and iDevices shrinks every year.
Devs and to a lesser extent users don't really think that way though.
It doesn't really make sense. iOS games are built to be played directly on the touchscreen. That rules out a lot of types of games (imagine playing WoW without a keyboard). It's not just about horsepower.
I do think Apple thinks that way but there's a good reason for Devs not doing so.
It's often said that macOS/iOS supporting Vulkan would help and while I think that's true to an extent, native Vulkan support is still rare enough that it's not going to change all that much in terms of ease of porting. It might improve things on the front of running games through WINE (DirectX → Vulkan translation), but unless developers produce ARM builds of their games there's always going to be the overhead of being run through an x86 translator, which varies depending on how CPU heavy the game is.