GraFx2 and TVPaint have a tool that is like outline-select automatically followed by immediate fill with FGcolor. It's extremely good for quickly blocking out masses; you can see moatdd using it a lot In this video-tutorial

Is there any better way than, well, "outline select followed by fill with FGcolor" to achieve this in Krita? Because it's much more clunky with the two steps -- everything takes more concentration and time to get right.

Contour fill's actual behaviour is slightly different from outline-select with regard to when the outline crosses itself. Here's a quote of Ilija Melentijevic

1. Contour Fill
A feature in pretty much all Amiga programs since DPaint. It is one of the freehand
modes that works like a continuous freehand but when you release the mouse button, it
connects the start and end point and fills the contour you drew. It has a somewhat
unique behavior when you intersect your contour. Please see attached image for
example. This tool is useful for laying out an image in standard paint mode.

In the image (found at the above link) you can see that there are never any 'holes' -- when the outline crosses itself, the hole is filled instead of being left a hole.
In SVG terms, this is using the 'nonzero' fill rule rather than the usual 'even/odd' fill rule

(relatedly, the shortcut keys to change FGcolor brightness don't seem to work in outline-select mode, even though it's definitely still relevant then. Makes consecutively laying down some blobs of different values slower than it could be.)

Hi,

Such filled shape can be done in Krita using the "Experiment engine" aka "Shape brush" ; look for default presets with Shape in the name

Ah, fantastic! Thanks so much!

(Krita is so full of stuff I wonder if I will ever get to understand even most of it

Actually the experiment brush doesn't seem to quite do the job, as it only uses even/odd fill rule, resulting in the creation of internal holes in more complex shapes, suitable for intricate things like flowers, while contour-fill uses the nonzero fill rule, which is more suitable for creating unholy* shaped blobs.

It's still a step up from my previous process, though

* There was no resisting that pun