Oilers have an answer to LaFleur, his name is Esa Tikkanen.
Tikkanen was not even the best defensive player on his own team, let alone enough to stop Guy Lafleur. Certainly not to the degree Gainey(Top 5 all time Defensive forward, arguably the best ever) could stop a man.
Besides which, the Habs squad of the 70's had an entire line of pest/energy players like Tikkanen. The kid line would have proved much more effective than Tikkanen. Not a single player on that line would have been intimidated by Semenko or McSorely, and that whole line was great defensively while fully able to each pot 50-60 points on the checking line.
In all truth, Tikkanen was a good pest, and could score decent(Although his numbers were Inflated by playing with Gretzky/Kurri or Messier/Kurri), but he would have been outnumbered by the kid line.
Throw in the fact that the Gainey/Lemaire/Cournoyer line was dynamite two way as well, and the oilers scoring would be mighty hard pressed to get things going.