The only "noob combo" aspect of the SC is SC'ing into someone and then finishing them up with the AR/precision weapon. Problem is that when you do the SC, you can miss if the enemy trusts/jumps/moves out of the way, punishing you with the wind down for missing, and the opposing player can just as easily, thanks to the radar, react to you coming, put shots in you, and then finish you off.
Getting caught off guard can feel cheap, but that's with any aspect of Halo. With radar, SC isn't that much of an issue, and even if you get hit, you still have the option of running away or getting a reversal.
Also, say there was no radar and SC was removed. You still have the same "issue" in that out of nowhere an enemy can sprint, melee you, and then finish you off with either another melee or just getting a headshot.