Considering the tools developers use in general (Visual Studio, VS Code, Eclipse, IntelliJ, Netbeans, various DB browsers, etc.), application start up time doesn't seem to be an important concern for the majority.

My IDE stays open (I keep all the common projects I work on open and just switch between them as needed). I rarely reboot. Startup time is completely irrelevant.

You typically leave an IDE open most of the time, and maybe start it up in the morning at most a few times a week.

For that, a cold launch time of a couple of seconds (VS Code) is fine, tens of seconds (Eclipse, XCode) is annoying.

Opening new files definitely needs to be instantaneous.

Yeah turns out the language server and other IDE features are resource intensive. Who knew. TextEdit also starts in under a second.

Why not starting them asynchronously? That's how Neovim does it. The editor starts instantly and the language server integration is enabled once the language server is active.

I use Vim with a language server and 10 other plugins that give me almost everything JetBrains offers. Only thing JetBrains is so much better at is fixing merge conflicts. Vim still starts instantly, and I never have to wait for it to index anything.

JetBrains is amazing, but I hate waiting for it. It stops me from starting work. Maybe that's just my problem.

On a given workday I always have at least one window of vscodr open that makes opening new files much faster than a cold start like vim et al are used

Once vs code and similar are up, the observed latency in opening additional files is what matters to most devs though.