I hope you're not suggesting that your ability to observe poll workers means that paper ballot elections can't be rigged.
It's not impossible to change votes on an individual level, but all the attacks against it don't scale at all.
How many votes do you need to sway an election? There are about 50 precincts in my county, which is one of 67 counties in my state.
Even if you somehow manage to rig each precinct flawlessly, that's still a lot of people that have to know about the rigging, over a pretty large area, and not one of them can get caught or the whole thing is over.
And if the elections are done right, there should be a number of people from the public at each precinct watching those ballot boxes all day, counting along when tallying votes, and ensuring nobody casts more than one vote or tampers with the box. Hell, you don't even need to speak english or have gone to high school to help secure an election like this, literally anyone can do it.
Paper ballots don't break down, they don't have glitches, they don't require 24/7/365 security to prevent tampering, they don't require nearly as many ballot workers or helpers, they can't "underestimate" voter turnout and only have 2 machines in a precinct to make people not want to wait hours to vote, and they aren't going to be able to be hacked by one guy at the dock yard alone with a shipping container full of voting machines.
It's not perfect, but it's a hell of a lot better than voting machines, mechanical or electronic.
Of course voter intimidation is a threat, but that doesn't have anything to do with the process of casting and counting ballots.