Okay since people don't think my posts are constructive enough, then I will use Smogon's official Tiering Policy Framework to show why dynamax & gigantamax needs to be banned. The Policy Framework is stated here.
https://www.smogon.com/forums/threads/tiering-policy-framework.3628026/
First of all, maxing is part of the actual game and like most mechanics,
tiering council wants to avoid banning it or putting a clause on it- see the example they give with sleep clause and freeze clause.
The mechanic has to be so gamebreaking that it warrants a ban.
Probability management is a part of the game
Critical hits, accuracy, secondary effect chance are all things to be considered in pokemon battles. However, factors that affect the outcome too much are not okay. People have accepted that maxing allows a less skilled player to turn the tables against a better player, and snowball the game to their favor. Furthermore, dynamax's stat boosts last until the pokemon is KO'd or switched out, which can be a considerable amount of time of disadvantage for the more skilled player.
Team Building- Dynamaxing forces people to put certain pokemon like ditto or play defensively and thus limits the team building options that people have. Ditto is almost a must pick and so is a valuable dynamax mon which already takes up 2 slots.
Battling Skill- Due to dynamaxing's interaction with the choice items, scouting choice moves with protect can become a non-factor and instead of switching, players can now dynamax and attack the opponent who will think they are safe. Dynamax moves do damage through protect and similar moves, and have 100% guarantee of their effect. So, even if people use the right move or predict correctly, they are still punished.
Broken- They are broken because they almost dictate / require usage, and a standard team without one of them facing a standard team with one of them would be at a drastic disadvantage. (directly quoted from the framework post)
As we all know, we are forced to dynamax in the current metagame, and thus dictate what the game should be. The OU metagame now centralizes around dynamax and players are forced to use it AND forced to have a team that can respond to the other player dynamaxing.
Yes, the meta always centralizes around something like megas and terrain, etc BUT in those formats, multiple forms of those existed, and none were dominant enough to dictate or limit the amount of options the player had.
In USUM meta, all four Tapus were OU and multiple megas were in OU. But, in the dynamax era, the metagame now revolves around a few pokemon.
Finally, their first goal and purpose
To create a metagame that is conducive to the more "skilled" player winning over the less "skilled" player a majority of the time.
This is the nail in the coffin. One reason why people like dynamaxing is the fact that it can often turn the tides of a battle. A player who was winning can lose to someone who is less skilled than them.
Comeback mechanics are an exciting part of any game, but not when it has nothing to do with the player's actual skill and more from the player's sense of desperation. I'm certain that with the advent of dynamaxing that comebacks have increased in percentage.
Comeback mechanics in pokemon were always pretty rare and relied on some really dumb luck like multiple turns of paralysis in a row or a lot of lucky crits.
With all that said, dynamax is an important part of sword/shield and the plot relies on it, and it is also the game's main selling point- using dynamax pokemon in raids and in entertaining battles. and yes, it does need to go away due to it going against the tiering policy framework.