Dynamax doesn't seem that strategic to me, the only thing you have to do is to be sure to dynamax one turn after your opponent
>Turn 1
Opponent dynamaxes and kills your mon
>Turn 2
Choose a poke that checks/counters the adverse mon and dynamax. The enemy mon is now killed, forced to switch or/and does next to no damage to your mon.
The opponent wastes the rest of their dynamax turns here
>Turn 3
Destroy/seriously weaken the adverse pokemon with your second dynamax attack
>Turn 4
Destroy/seriously weaken the adverse pokemon with your third dynamax attack