Additionally, the lack of an item restriction means it has a much lower opportunity cost when it comes to team building. With Megas and Z-moves, you had to choose them while team building. Using Mega Scizor meant you couldn't use Mega Mawile, and using Z-Kartana meant you couldn't use Z-Magearna. Well, technically you could, but it was a bad idea because it ensured that one of your Pokemon would have a useless item in every game.Important thing to note about dynamaxing- anything can do it, with no item restriction. This means you can choose what you dynamax on the fly to counter an opponent’s dynamax. A lot more nuance compared to “My Heatran will now beat water types with this item” like Z moves were
With Dynamaxing, all six of your Pokemon can do it, with the ONLY condition being that once you power up one, you can't power up the others. This means that even in the builder, you can effectively design a team around multiple Dynamax Pokemon. "If I'm up against offense, I'll dynamax Dragapult. If I'm up against balance, I'll dynamax Hydreigon." Once again, you could technically do this with Megas and Z-moves, but it wasn't very popular because of the item requirement. And unless every member of your team had a mega stone or z-crystal, you were never allowed to deviate from your initial gameplan in battle quite like you can with Dynamaxing. "I may have designed this team with Dragapult and Hydreigon in mind, but if I dynamax Frosmoth right now, I win."