Vim is not instant. Moreover, it has annoying TTY handling behaviors; it flushes the TTY when starting.
So if I type
$ vim file
and start entering editing commands, often I do it so fast that some of the characters get cut off, like the leading colon of an ex command or what have you.
There is no good reason for this. It will not happen with any reasonable command line utility.
I reported this to the Vim mailing list not long ago and was basically brushed off.
What's missing is the statement that this is how things work when one is relying upon terminals to respond to special control sequences with strings denoting their capabilities. In theory one could save up and re-process the input characters that arrive before the DECDSR response. In practice, people throw them away.
Did you try it on a non-xterm terminal type, as was suggested?
Have you reported it to the Neovim devs? It stands a better chance of being included there (IMHO) and from there it's possible that it trickles up (like the async features in Vim 8).
I love vim but recently started using Emacs with spacemacs and it takes a long time to load. Vim is basically instantaneous and Emacs is like molasses.
Use autoloads everywhere. Put all per-package configuration in lambdas executed on hooks, or eval-after-load. Lazy-load Helm by mapping M-x to helm-M-x etc. - small ad-hoc edits probably don't even need Helm.
I still use emacs --daemon / emacsclient (aliased to 'e'), but I keep my $EDITOR set to emacs. There's no good reason to have a long wait for startup.
Well I certainly don't dig into the depths of what I can make emacs do (and hence load) but I find it opens seemingly instantly for me unless I am doing something like using the window mode on a VM that mimics a video card.
Emacs user: You should never turn off emacs.
Vim user: because it takes too long to load emacs.
The irony being the points behind both sides of this joke pretty much have no meaning with the current state of technology.