Well I guess you need some basic background about traditional japanese knives. Traditional knives, the single bevel kinds, and all have very specific tasks. Usuba for veg (different techniques than you though), deba for breaking down fish, yanagiba for slicing fish.
Santoku was introduced as a multipurpose double bevel knife for all the tasks a home cook might find. Unless you're a weirdo like me, the average home cook doesn't want to have 2 dozen different knives for different purposes and most of them want no part of serious butchering or fish breakdown. Mostly santokus are too short for me. Try working with a cabbage or a melon or slicing a big roast and tell me if it's long enough.
Chefs knife is the western version of all purpose knife. It's okay at everything, but there are always specific knives that can be better. Still, I use it for 90% of kitchen tasks.
If vegetable knife means nakiri, that's a double beveled usuba. It's meant for normal cutting of vegetables and can't do the fancy paper thin garnishes you can do with usuba. I would say it helps because it has no tip. If you run low on board space, you'll understand.