The major factor Apple has working in their favor with regards to the future of gaming on Macs is iOS. Any game or game engine that wants to support iPhone or iPad devices is going to be most of the way to supporting ARM Macs for "free".
My older Intel Macs I'm sure are more or less SOL but they were never intended to be gaming machines.
That won't get the top 10 Steam games running on MacOS. There's just too great of a disparity in the tooling, a 'convergence' like you're describing would take the better half of a decade, conservatively speaking. And even if they did converge, that's only guaranteeing you a portion of the mobile market, and just the new games at that. Triple-A titles will still be targeting x86 first for at least the next 5 years, and everything after that is still a toss-up. There's just too much uncertainty in the Mac ecosystem for most games developers to care, which is why it's a shame that Proton doesn't run on Macs anymore. Apple's greatest shot at a gaming Mac was when MacOS had 32-bit support.
Your older Intel Macs are probably just fine for gaming, too. I play lots of games on my 2016 Thinkpad's integrated graphics, Minecraft, Noita, Bloons Tower Defense 6, all of these titles work perfectly fine, even running in translation with Proton. If you've got a machine with decent Linux support, it's worth a try.
Unreal, Unity, Lumberyard, and Source 2 all support iOS and thus Metal on ARM already. A game developer using one of those engines should generally be able to just click a few buttons to target an additional platform unless they've gone around the engine's framework in ways that tie their title to their existing platform(s). Obviously in all but the most trivial cases there will still be work to be done, but those game developers using a major commercial engine are doing so because someone else has already done most of the hardest work in platform support for them.
That means six of the top 10 could add native MacOS support with relative ease (as in significantly less work than doing it from scratch) if they wanted to. The three Source titles are likely stuck on DX/OGL platforms forever because it doesn't really make sense to rework such an old engine, but at least the two Valve in-house titles have had persistent rumors of a Source 2 update for years.
I mean…the “tooling” these days is usually just Unity3D. And Unity supports Apple silicon as a compile target. Tell me if I’m wrong, but it seems like the ability to support multiple platforms and architectures in gaming has never been easier.
> iPhone games are an entire different beast however, and likely not what people “want”.
Most of those mobile games you're thinking of are made with Unity, Unreal, or one of a few other general purpose game engines. Those same engines are used for a significant chunk of PC games as well. The AAA developers who have in-house engines like to reuse them as well. It doesn't matter if a given game does or does not support mobile if it uses an engine that does.
My older Intel Macs I'm sure are more or less SOL but they were never intended to be gaming machines.