This is pure bs. That vid is of some random early gloved idiots.
We only have one clip of an old Sullivan doing some shadow boxing.
First up you can't fight in the modern gloved style exactly like in BK.
They fought further at range and used the front hand to parry down body shots.
The used mainly straights to the body and face to not break the hands.
You would probably break your hands on their heads if you came in swinging.
The style is actually similar to WC with punches I think there is a connection.
https://www.wcarchive.com/articles/armando-sainz-revival-bare-knuckle-boxing.htm
You can't discount how BK boxing evolved over a 100 year period before the modern era and you have no reference point apart from the recent modern BK fights we have to say you could go in a time machine and clean house.