A spartan can flip a tank in the game. They kind of had to add that mechanic so you could continue to use them if they flipped. In the books, they have never done such a thing. Ever. I doubt they even could. Hell, theres no way a spartan II could even flip an elephant, yet they added that mechanic in the off chance that you were ever able to flip one in the first place. We're going off books here, not games dude.
And if you believe a spartan can take a lascannon shot and live, then I have bad news for you as well. A spartan with shields has never been able to take a head on fuel rod shot and live. Only one spartan two lived through it, and he had a jackal shield in front of him, as well as his own shield. And he lost an arm in the process, and was in shock afterward. It would do a space marine quite a bit of damage to his armor, and the flesh underneath, but he'd get back up and be pissed as ever. A spartan II would be dead.
John got lucky with the air-to-surface missile, because he had Cortana's help in calculating what it would take TO deflect it. He even did himself a shit load of damage in the process. Even says that he got lucky in the book, IIRC. If he hadn't had Cortana, he would have died on that training ground. I'm not saying a space marine could do it, because I highly doubt he could. They'd both be just as dead. But John having the help of the smartest AI around helps a helluva lot.
If the spartans weren't in the direct line of fire (i.e., in their own element (i.e. their own terms)) sure they could take a hundred+ covenant and come out with a few scratches, burns, and dents. In the direct line of fire, they'd be dead like any other. A space marine would be wading through, letting his armor soak it all up, and would be able to take a few down with him. In his own element, on his own terms, theyd be dead, and the space marine would be even less harmed than the spartan.
Anything I missed? No? Good.