Most of the men in the historical portraits and photographs you see are wearing clothing that was made for them - i.e. to their measurements and body shape.

The phenomenon of going to a store and buying clothing made in a "standard size" off the rack (and hoping it will fit you right!) is a relatively recent innovation, historically speaking.

The truth is that very few people come in a "standard size." Everyone is a little bit different. And even if we think that a standard size fits "well enough" part of that may simply be how we have been conditioned by years and years of wearing standard sizes. This is how we "think" clothes are meant to fit.

I recently had a shirt tailor made to my measurements. It fits rather snugly compared to the many shirts in my closet that were purchased off the rack. But it fits well. I can move around easily in it. So in no way would I say it was "too tight." But rather, all my other shirts are too loose in one area or the other. To get the right neck size and sleeve length that I require, my shirts are typically too large in the bicep and around the waist. I've just gotten used to it, because that's how standard size shirts fit on me. Until I had a shirt actually made-to-measure, I didn't know the different.

I suspect something similar may be what you are noticing in the waistcoats.

That, and I notice that even today American men tend to wear their shirts and jackets much in a much looser fit than their British and European counterparts. This is why many American men are advised to "order a size up" when they order kilt jackets made in the UK. It's not that the UK sizing is measured any differently, it is simply that most Americans expect a looser fit in their jackets than British men do. We are not used to that tailored look.