The mob? The “mob” was just standing there when the police were ordered to fire on the “mob”

The mob had already broken through several barricades to get to that point. The police were driven to physically interpose their bodies to try to keep them from breaking into the Capitol building. You can see the group pushing against the police line, trying to push aside the police by force - and the police struggling to physically restrain them to keep them from breaking into the Capitol building.

You're looking at only a few seconds of slowed-down footage - and even in that, you can see that the mob (yes, the mob) is trying to break into a federal building and trying to physically shove aside the police that are trying to stop it.

So, no - this wasn't excessive force. The police used appropriate non-lethal tactics to disperse a volatile mob that had already broken through the barriers meant to keep them out of this space. The crowd was clearly in the wrong, the police were clearly in the right.