HTupolev

1-Slower because they were bottomed out and their pedaling form went lumpy.
2-They often just didn't. Letting your bicycle dictate your routes is a path of less resistance than fixing the bicycle to facilitate the rides you want to do. It's not like that doesn't still happen today, even with modern road gearing; the line is merely drawn at weaker riders and/or steeper hills.
3-If they really wanted lower gears on their road bikes, it was entirely possible. Wider-range drivetrains existed and worked great, and this has basically always been the case: derailleurs spent their first several decades being marketed primarily at cyclotourists. It just wasn't fashionable to use wide-range drivetrains on racing bikes.

If by "no matter what gearing you have" you're assuming that the rider is sticking with standard road offerings, perhaps. But if you literally mean "no matter what gearing you have", then I'd disagree. 20% on pavement normally isn't a very big deal if you're not bottomed out. Maybe if you're down in the <2W/kg range and your speed has plunged down into the realm of 2mph or lower and you have balance issues. But most people can keep a bicycle balanced at those speeds pretty well if they're rolling power through the cranks.