This is not the source on which Garrys mod runs, it is the unreal engine styled to mimic the source with its limenality, so this is not a bunch of assets, but a game made from nothing, and it is not made by professionals with a large team of developers, but by enthusiasts, hence such a big difference in performance.
About the “Death is near” event I can agree, players who encounter it without knowing what it is often think it's some kind of glitch, and it's not cool tbh, so it seems to me that there should be something that explains what to do in such a situation, perhaps more detailed messages from arirals.
But about the tutorial I strongly disagree, it seems to me that to literally lead players by the hand showing all the game mechanics and features is bullshit, then what is left for the player to do in the game itself? to follow the instructions? Isn't it more appealing to spend 15 days at the base doing different things, after which you'll think “Oh, what a dump this is, is it a research complex or what? I should clean it up, I think I saw some garbage bags at the store...”?