Reddit mentions of Avantek Laptop Cooling Pad (83A)

You've clearly done your research so good job there. I've played the game on a laptop since launch as well, and just like you, the performance started out great, and dropped after a while.

Great ventilation doesn't prevent a dust buildup over time. Try compressed air. You might be surprised by the results.

Have you checked your temperatures when the performance tanks? I've been using my laptop with a cooling pad for a year now and it has helped a lot over long gaming sessions. Check your temps to narrow down the issue further. Good luck!