Very interesting responses, really! Thanks for your input!

The bikes are: an early 70's Legnano Corsa, late 70's Mercier tour de france, and an other early 80's pegeaut for which I don't have much info.

Someone mentioned safety levers, and indeed the mercier which seems to have the weakest brakes has those (I don't know but for city use those are great, atleast for me). So, maybe it is indeed that!

Also, the housing and wires might be factors in the problem as well! I'll check it out!

The truth is I haven't had much experience with modern road bikes, so I can't affirm the knobby tires=better braking theory. It makes sense though.

NOW I'm guessing that, these road bikes have small pads and old, so not so efficient, calipers. Also old brake levers aren't that solid. Adding skinny tires and more aggressive sitting position, it creates a feeling of bad breaking. That's my theory.