>>40887318No, they're weaker than Z Moves, the issue is that you get to fire off 3 of them and they have added effects like boosting stats, lowering the opponent's, and setting up weather and terrain. The big guy also enjoys being 50% harder to ko for 3 turns.
Dynamax is somewhat balanced by the 3 turn limit, all status moves turning into Protect, being able to only be used once, and switching your big boy out gets rid of it.
You can stall out a Dynamaxed opponent, but it's theorized that they will still be use thier Max Moves to set up and then you'll be in a world of hurt even after they've returned to a normal size.
Say I'm using Kommo-o, I can Dragon Dance up to boost my attack and speed by +1 while you switch into say Toxipex. I can then either go for a Max Fighting, and boost my attack by +1 each time I attack or I can go for a Max Ground and deal some big damage. The fact that Max Fighting is essentially a Z Move and Power-Up-Punch combination is really threatening.
A Dynamaxed Hydreigon can just click Max Dark Pulse and your switch in is at -1 Sp.Def and it's going to go down to the next hit as Hydreigon will be packing coverage moves. You're best bet would be to send in a dark resist, specifically a Fairy, either protect or switch to something that can take the coverage max move, then go back to your Fairy type. Sure, you may have not lost a Pokemon by triple switching to stall out Hydreigon, but your Dark resist is probably ar low HP, as is something else and there are now holes in your team's defenses.