Vulkan support is now there (it was added in the last couple of years). Might not be for all engine branches though.
Given that the engine has been in, essentially, maintenance mode for almost a decade now, that is not really surprising. A more apt comparison would be Source 2 I assume.
> some events can take half a second to make it from a player's action to another player's system
What are events here? At least in normal source this should be impossible for anything movement/input related as the server processes the input each tick and then distributes that to each client (the Apex implementation should still do this). If it takes half a second to forward such an action, the whole server should hang for this time in the eyes of each client.
> The game's input processing is done in relation to framerate
This is a behavior added by Respawn, not something normal Source does.
> The security and anti-cheat in the game is so hamstrung by Source
That is a really broad claim imo. AFAIK CSGO only had this issue once in its lifetime and that was caused not by an issue in the engine but in the matchmaking service. So isn’t it more likely that Respawn just screwed something up?
Do you see Source being used in virtual soundstages? No. Does Source support Metal or Vulkan? No.
Does it have anything approaching the 3D or 2D or rendering style capabilities of any modern engine? No.
Is Source going to be remotely relevant for metaverse stuff? No.
All the money in the world won't change the fact that Source is an outdated pile of garbage.
Respawn uses it to this day for Apex, and it's horrific. Its graphics quality is atrocious especially for the demands it places on hardware. It has the worst latency of any similar multiplayer game (some events can take half a second to make it from a player's action to another player's system!) It lacks modern features that have been in other games for many years, like variable event rates (some games, for example, will use much higher event update rates for stuff happening within the player's field of view.)
Its game engine has so many bugs around inputs, movement, and collisions that high level play revolves around abusing all of them for competitive advantage in what is lauded as "movement", and because Respawn never treated these issues as exploits, they got painted into a corner where they can't ever switch to a modern game engine because trying to get the quirks of movement behavior would be impossible.
The game's input processing is done in relation to framerate, for fucks sakes....so input processing behavior changes depending on framerate.
The security and anti-cheat in the game is so hamstrung by Source that multiple world tournaments have been hacked live and ultimately had to be done in secret, later broadcast - because Respawn was so powerless to stop the hacker(s).
With more Unity shifting to a royalty model you're going to see a lot more interest in open source game engines like Godot; Godot is, for example, working on being usable for massive multiplayer and open-world games.