I am not sure whether this is bug or design decision so I’m posting it here first.
I have two pointing devices which I use with my laptop — built-in touchpad and external USB mouse. In activities view, when my cursor above workspace switcher or just windows thumbnails I can switch between workspaces by scrolling using
a) edge scrolling or two finger scrolling on built-in touchpad,
b) or wheel of external USB mouse.
In b) case scrolling is just ideal. With small but reasonable move of mouse wheel I can switch between workspaces. But, in a) case switching between workspaces is VEEEEEEEEEEEERY sensitive. To be honest, it’s just unusable.
I am able to reproduce it with Fedora 30, Ubuntu 19.04 and Arch Linux. Do you have the same issue?
Edit: I should also mention that I have no problem with scrolling sensitivity in GTK apps, Qt apps, Firefox and even in application menu extension of gnome-shell. It’s specific to activities view.