I personally really dislike it as it will probably lower top player win ratios by making worse players win more often from a singular lucky guess in initiating a dynamax at the right moment because now suddenly one single decision/guess very often decides entire games due to how powerful and polarizing a mechanic it is. There will also come times where you correctly predict a Dynamax, take your best possible course of action to deal with it, but due to Pokemon RNG you will often fail due to things like missing attacks, allowing your opponent to potentially now sweep your entire team with Dynamax for absolutely free, again further making it more luck based and less consistent than the game needs to be. This is the farthest we've strayed from gen 4's fantastic metagame to date because the difference is like night and day, whereas gen 4 is like Pokemon's chess, gen 8 is its poker. At the end of the day it really comes down to your personal preference whether or not Dynamaxing makes the game "better" for you, but I personally think that a mechanic with no drawbacks that makes one single decision usually dictate the entire outcome of the match is pretty bad considering how long Pokemon battles can be and how frustrating it is to lose that way after a long match of consecutively outplaying your opponent otherwise. It also doesn't help that speed has ALWAYS been the most important stat (I don't know anything about gens below gen 4 though) and that this mechanic only further makes a high speed stats in particular even stronger. At the end of the day however, it doesn't really matter for anyone not playing VGC rules because Smogon can just very easily create both a format for dynamaxing being allowed and one for it not being allowed and everyone can just be happy playing what they want to.
