Response Speed. Most emulations tend to fall behind my actual Vim command speeds, which really destroys the vim editing flow.

Occasionally emulators will not honor mode switches correctly or on the first try. So I would expect to be in insert mode after a complex set of commands but the emulator isn’t there. This is also likely due to speed issues, but maybe not.

Emulators do not do a good job of handling macros, and vim’s repeatability. The auto stuff they try to do (such as formatting, etc) precisely the reasons one would prefer an emulator, can mess up repeatability.

Many of them don’t handle certain basic commands. A lot of emulators, for example, do not handle commands like HML which shift the viewport, possibly because the IDEs do not really give them access to it, or maybe because they aren’t known well enough that they fall way down the priority list.