Here's the thing though. Dyna/Gigantamaxing occupies the same niche that Megas and Z-moves used to occupy, but in a more nuanced way, which is far from just tossing out other mechanics because they were unpopular or for the hell of it.
Megas were a good idea on paper and let some low-tier mons shine, but they were just too powerful on average to the point of completely overshadowing the base Pokemon, which just raises the question of why they don't buff that if the only good thing it can do is Mega Evolve. And then we know what happens when given to already good Pokemon: they get put in a class of their own at worst (Mega Rayquaza).
Meanwhile, Z-Moves were strong, but their one-time only use in a battle severely limited the possible applications they could be used for. Either they were just standard nukes, or at best your whole strategy hinged on one like with something like Z-Splash.
Here we have transformations anyone can use, with powerful moves that do more than just cause a lot of damage, but with tweaked stat boosts and a more reasonable turn limit that prevents them from singlehandedly carrying you to victory. Even for the ones blessed with a Gigantamax, they mostly amount to having an extra tool in their box rather than being a huge privilege. I'm of the mind that if your goal is to drastically boost a Pokemon's viability, mundane solutions like boosting their characteristics or regional forms are a better way of going about it.
It's too soon to say if Dynamaxing, or at least the mechanics behind it, will stay as they are, since we still need to see how they shake out in the meta, but the general idea behind it has stuck for three generations so far so it's unlikely it will go away for good, regardless of whatever form it may take.
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