There should be an option as follows:
Whenever i enter insert mode, just switch to native Qt Creator input, with the exception that ESC returns to command mode.

don't know how easy this would be to implement, but for me it would be a huge usability improvement.

All the usual editing shortcuts would work, e.g. shift-tab to unindent, ctrl-backspace to delete word, etc, plus qt specific ones like CTRL-R to run, CTRL-O to open, CTRL-N new file.
Also, you could get rid of the comma stealing, which would be nice for navigation.
And since (AFAIK) vim doesn't do anything special during insert mode, there is nothing lost.