I don’t know why the vector fill gradient doesn’t work on text but it doesn’t so it would be a good idea to raise a formal bug report for that.
The layer style gradient overlay seems to be a ‘broad brush’ effect but it does work at doing what it does, as far as I can tell.
If you select the text and switch to the Edit Shapes Tool, you can Convert To Path in the Tool Options docker and then it becomes a vector object that you can put controlled vector fill gradients on. It’s not text after that so you can use a copy of the text object to do that on.
In your video, copying from Inkscape does seem to work in that you copied a vector text object and it was pasted as a vector object. Was it text that could be edited? I noticed the colour change - is that what you meant or have I missed something?
[On my Linux system, that gives me a pasted paint layer so there’s some system level clipboard strangeness going on for me.]
David Revoy’s speech balloons were made in Inkscape (or similar) and exported as an .svg vector library for use in krita.
He might come along and tell you about his processes and workflow for other aspects of his work. Maybe you could poke him with an @
I think that a ‘safe and guarenteed’ way of working with Inkscape is to produce completed vector artwork and then export it as a .png file for import into krita.