Spoof Command makes the device think you are the OWNER of the Device, which is naturally much harder because the Owner is at the unreachable 4 Marks level. We're talking about registered, legitimate users here, not the owner. Only 1 person can be the Owner of a Device, but when talking about a secure facility many people will need to be able to access the commands and input orders to do their job. Your line of reasoning does not hold true. I'm also not talking about just 1 mark (at which point many advanced functions should rightfully be locked from you) I'm talking about having 3.
Jump Into Rigged Device (the corp owns the device, the security rigger is an authorized user) suggests that I am correct by virtue of the fact that it's an opposed roll. Under your theory, simply having 3 marks would be sufficient to perform the action without the roll. Presumably, the authorized rigger doesn't roll vs. Firewall + Willpower (does he use his own Willpower?) in this situation.
To a certain extent, marks exist simply as a game mechanic to make decking work a certain way, but for the sake of verisimilitude, think of it this way: PC generated marks (as opposed to host-generated marks) simply aren't as good. Maybe this is because they aren't stored in the host's "authorized user" file. Or whatever. But there is no scenario in which an authorized spider and a decker have precisely the same ease of function. An authorized user can Control Device no problem, but for me to attempt to slice a small piece off of the host's WAN, I need to have 3 marks and even then the host isn't going to go along willingly.
Understand: I'm not suggesting you should be able to do anything and everything with 3 Marks on a device, but as the rules currently are you can't do anything legitimate with it.
What Shadowrunner is interested in legitimate activity?

I think of marks not as what sort of legitimate actions can my decker take, but rather what depths of illegitimacy can he reach? He'll never be a legitimate user. He can kind-of-sort-of fake the host out for a little bit, but the nature of decking is that sooner or later, the clock will start ticking. Maybe he'll send everything into reboot, log out and log back in to reset his OS, but he can't live in the host 24-7, no matter how many marks he has. Even doing nothing at all with 3 marks, he's going to accrue OS every 15 minutes.
The Control Device action, at least, should use Data Processing when you have 3 marks, not Sleaze. That still leaves every other matrix action wide open, and Control Device only deals with devices that interact with the meat (doors, lamps, locks, turrets, etc) so there'd be plenty of stuff to do besides plant 3 marks and be done with it. It's not that easy to get 3 Marks on a decent host anyway.
I understand the thinking here, but if Control Device didn't generate OS, a decker could get his 3 marks out side the host (fail a roll? log out and log right back in), enter the host and then perform DP actions that could literally kill the entire staff of the building without any risk of generating more OS. Presumably a spider shows up at some point, but it still throws the entire thing out of whack and goes against the design philosophy of matrix rolls being like meat rolls (in this case, opposed rolls to control something).