...where to begin!
So much was wrong with cantilevers and linear-pull came along and made the cycling world a happier place.
This list will grow, but, as I remember, the following things were morally wrong with cantilevers:
the front cable often routed via the stem on a pulley hidden inside the stem. Over time this pulley would fray the cable and the cable would break on the front brake with no external signs of anything wrong.
Unless a reflector bracket or mudguard was in the way, the broken front brake cable would release the stirrup wire to then catch against the front wheel. This would cause an instant straight-over-the-handlebars disaster.
Even in peace-time the arrangement was not too good, the brake adjustment depended on stem height.
Some bikes did not use the stem to hold the front brake cable. Instead they used an extra bracket in the headset. When suspension came along a bracket had to be added to the forks to hold the cable.
The bolt at the end of the cable holding the yoke that connects to the straddle wire was also a bit of a problem. Typically these were setup crooked. In use the stirrup could get knocked to one side, compromising the brake balance.
As for the rear brake, the big problem on early models was how they stuck out to catch your heel. This was solved when Dia-Compe came along with the 986 to replace the 983. Shimano copied the hi-rise idea shortly thereafter.
Here is a 983:
And here is the 986:
We are talking twenty+ years ago with this 'big change' to the cantilever. There were many, many iterations to get to the linear-pull brake you have today.