The distances you’re talking about, underseas cable from continent to continent, even terrestrial cabling across North America, are already fiber optic. You may have heard of players using VPNs to reduce ping. They’re not defying the theory of relativity when they do this. They’re just transiting through less busy (by virtue of being semi-private) and less (by virtue of being arms of a single layer 3 network spread over a long physical distance) routers.

Devices like you’re mentioning for signal amplification are largely stateless and take “basically no time” to do their work. There’s no decision tree, it’s just “make it louder.” Routers, firewalls, and to some extent smart switches and the like have real processing time burdens. It’s all a really interesting topic if you want to nerd out about it, and I think it’s great you’re reading up on it. Just try to filter out the noise (typically, what ISPs, content providers, and politicians are telling you as a retail consumer).

To bring it back to game engine design, the question on the mind of a content producer like SE (besides “can we just pay to get on a better carrier?”) is “what can we do with the network available to us?”

The global cooldown and what we know as “animation lock” are soft answers to this: make it irrelevant how fast a player mashes the key. The input buffer at the end of your GCD is a hard answer: accept that lag is a part of network communication and solve it gracefully for the player. All sorts of these things are running in games and are designed to be as invisible to you as possible. There’s motion prediction to have your character continue on the last direction the game received input data for, until a very brief timeout expires or the game hears from your client again that you stopped moving or pivoted. Some games do this client-side (think Ultima Online and rubber-banding. When the client hears back from the server that it didn’t accept your movement, it slaps you on the wrist and sends you backward) and others do it server-side where the server allows a degree of leniency and when your client says “I spent the last 30ms moving north and got 2 steps” the server decides “ok, that’s feasible” and updates its record of your position to seamlessly match the client.