[bjourne]

Yes, you could very easily do that. However, the theory is that cheaters would let the engine decide only 3-4 critical moves during a game and that would be enough to turn the tide in their favor. In chess small advantages compounds so this computer help would be enough for grand masters to beat the world champion. A cheater that understands cheating countermeasures could easily fly under the radar that way.

[sgjohnson]

The problem with this approach is that you'd still need to be able to correctly identify those critical moments in the game, and a single move won't help you. You need the entire line.

Which would still require a considerable skill. If you can't figure out why a single move is brilliant, you won't be able to find the entire line.

If stockfish tells you the entire line, and the opponent plays something that wasn't included in stockfish's line (because it's worse), you're also going to be at a loss.

[ciphol]

If you're playing Magnus Carlsen, you're probably pretty skilled to begin with.

[tstrimple]

The best cheaters are also highly skilled. This is true in online competitive games as well. Very rarely do these folks just leave cheats on all the time. That's blatant and easy to ban. But toggling it on at critical moments will give you those "clutch" wins which genuinely happen sometimes, but makes them much more reliable.