Skiing

Depends on how good they are, as with skiing. I guess a beginner boarder might be slightly less in control than an equivalent skier in some circumstances, but not much in it I would say. Conditions also factor in - on ice skiers prob have a bit more control (at the equivalent skill level), in powder boarders will be a bit better IMO - on a bashed piste, pretty much the same.

On my best day I'm completely mediocre skiing and a bit worse boarding. Entirely on piste, never look graceful at any time. I will immediately defer to anyone that knows what they're talking about...

That said, as a complete punter, boarding feels like you're roughly as in control as you are skiing. Can get away with a bit more in some places (can be easier to get around on pistes that you might struggle with if it's icy on skis - albeit by scraping the snow off and pissing off skiers), and less in others - the random edges you suddenly find that land you on your arse come with less warning than skiing.

I found it different, but not necessarily more or less in control.

This could all be overcome if I knew what I was doing

As a snowboarder whose never skied I couldn't make a direct comparison but I think it's more a case of competency rather than the sport itself being less in control. If I want to head to a certain point of the slope or avoid people around me I can do that happily and if I need to stop for any reason, making a decision where to go at a split/an issue down the slope/end of the piste/immediate issue in front of me, I can resonably do that too without taking anybody out. You do definitely see snowboarders wiping out and taking others with them but I'd think they were not hugely confident/skilled personally with control yet, much like the beginner skiers who end up coming into the lift areas a bit too hot and such. On ice though it's a whole other game, can still control things but for me at least I just have to take it agonisingly slowly and the shins and calfs start to burn from the effort of not losing it so most fun is removed from the activity.

You can easily be as in control as when you're on skis. And realistically pose an equal risk to others on the hill.

The issue in my experience is as already mentioned - a lot of folk over estimate their ability (on both types), a lot of folk are not familiar with the other sport (your movement about the mountain is very different on skis to a snowboard) and the snow conditions: if it's ice and you're on a board you need to rethink life a little.

I've probably been taken out by even numbers of both clans, but have a definite bias against whatever the opposite is to what I'm on that day. And I'm sure we can all agree Big Foots and Ski Bikes are the real problem ;)