Yes, it would be different. LEO, and specifically Capitol Police, are trained in the use of their weapon as well as situational training.
Your average wannabe with a sidearm would just exacerbate the situation, likely causing more mayhem/casualty.
Also:
Bullshit. This argument is bullshit.
We've found a rare line where I'm vociferously disagreeing with you.
Most people who own firearms are not fucking Barney Fife. Most people are well trained on how to use their weapon. The notion that if one or more of those senators had a firearm on them then they would have just started shooting aimlessly in 360 degrees, killing/injuring more people than the shooter intended to is not only supported by zero evidence, it is completely preposterous.
That it "would just exacerbate the situation, likely causing more mayhem/casualty" as opposed to the complete absence of any firearms from the "good guys" is a Prowleresque braindead idiotic thing to say, frankly.