When I open the ready made startup file the brush size is the same as in your video, but when I use it it's not the same but too small. If I create a new file with the same settings the brush size is ok. how come?
I found the culprit! Stroke thickness scale on the grease pencil object is set to 0.10 (this was so it would look correct at cm scales). If you set this to 1.00 the stroke should go back to a bigger thickness. I can update the start-up file for you if you like. You can also fix this easily - make a new file, change this setting, save default, and the modification will be retained.
