Dynamax/Gigantamax is basically a combination of Megas and Z-moves. All Pokemon can Dynamax and have access to generic powerful moves that are big and flashy like the generic Z-moves, and Gigantamax are new forms like Mega Evolutions that come with exclusive flashy powerful moves like the exclusive Z-moves.
Not really the same. Dyanamax can be done only in certain location, it lasts for certain turns and replaces all your moves with generic moves.
Not every pokemon of the same species can giantamax, you need to find specific ones that can. They don't even get new abilties and the only stat that's boosted is HP.
They might be similar but there is still too much difference to make dynamax count as comibnation of z-move and mega evo.
