And then what? Once the mob was cleared out, they would have resumed. There's a chasm between disrupting proceedings and actually taking over a country. The latter also almost always involved having control of the military by the way.
It might've been a short civil war, but if Trump had gone out and marched with the protesters like they thought he would and told them to stay in the Capitol building, you would've immediately created a situation where government business is suspended and the commander in chief is at direct odds with the military's constitutional obligations.
There was, and has been, a soft coup ongoing since that day, since the president at the time refused to issue any direction to the military and situation only started to be resolved when Pence took defacto command of the executive without invoking the 25th amendment. That process has been ongoing since then.
Remember Trump is already commander in chief, so has power 'by default.' He just needs to create a situation where that status quo remains, either by creating a situation whereby the right people are willing to disregard the election results /or/ the constitution directly.
Second: As others have observed, we got extremely lucky that the rioters didn't actually come in contact with any congress-people or the vice president. What do you think would have happened if, say the crowd has come in contact with AOC, for example? What would have happened if enough Dems were killed or incapacitated to change the balance of votes on certifying the election? The hundred-odd house republicans certainly made a big point of not changing their certification votes after the riots.
Third: When someone fires a gun at your head and the bullet misses, will you make excuses on behalf of the shooter? After all, if they were /really/ a killer, they wouldn't have missed, right? The bullet missed, you continued on your day, nothing should be done...