Seems like most of these apps focus on features instead of getting thes basics right.
If I have thought I want to jot it down and continue, not wait a bunch of seconds or more to get going.
Google Keep opens in about a second on my phone, so seems to be the slowest of them all.
But I'm sure there are plenty of notes apps out there that also opens in sub 0.5 seconds, right?
This is not true, many apps (or maybe it's an OS thing) retain an image that is not functional, you should count until you actually type any symbol and see it appear in the app. This also differs between switching to a recently opened app (hot) and an app that's been closed/unloaded from memory, both of which matter for instant note taking.
If I wait ~3 seconds after typing I can see that the change has been persisted to the sync servers and it appears in my Obsidian desktop application.
And for hot start you shouldn't even need to tap in the document if you edited it before, the keyboard will already be opened, so the measurement is "time start, tap the app icon, tap any key, see a character appear, time end". This is a common workflow for app switching and copy&pasting from/to note app/other apps, so here even half-second delays are noticeable, and where Apple Notes shines (and only very few apps match that, but not Obsidian)
Then the cold start is where using other apps forced note app to be unloaded (or after a phone restart or "force swiping up closing" the app (think it has the same effect), here the performance difference between Notes and Obsidian is even more noticeable
But then we were talking about startup times...
You can see a comparison chart here: get-plume.com