Each time one uses the term "mass shootings" a definition should follow. When gun opponents talk of mass shootings it's not primarily street gun violence, it's school shootings and the like.
Now all these links put the shootings together in one basket and dispel mental illness as a major cause. Even your links do say that mental illness plays a part.
The below link says the handgun is the weapon of choice in "mass shootings" But again it doesn't separate the kind of shootings, much the same as saying mental health is a small percentage of shooters.
https://www.statista.com/statistics/476409/mass-shootings-in-the-us-by-weapon-types-used/
https://www.statista.com/statistics/476409/mass-shootings-in-the-us-by-weapon-types-used/