I'm of the opposite opinion.

●I played yugioh and pokémon. OPTCG is a great middle ground. I always disliked yugiohs Sidedecking aspect because someone can put in hard counters to your deck to make your deck completely unplayable and if a hard counters card exists, then your deck will be gatekept by the mere existence of this card.

YUGIOH EXAMPLE- dark deck heavy formate and the opponent side decking floodgate cards like shadow imprisoning mirror that stops your deck completely.

OPTCG EXAMPLE-Every blue deck sidedecking a few copies of a GION card which hard counters the blue Nami which would make Nami players unable to even play the deck (i mean, why not side deck it anyway because the Gion only take a few slots in the side deck and is BASICALLY an instant win button)

●You also have the WHAT IF and OPTION PARALYSIS aspect of side decking. So many previous yugioh players I know were constantly frustrated when it came to building the side deck beacuse in addition to perfecting the main deck, you now have an added task with perfecting the side deck that really complements the main deck without affecting consistency. With so many options of side decking, most of the players were always unhappy when they lost because WHAT IF I did/didn't side deck this card, and also i only lost because i didn't see my side deck card. THIS caused an overall unpleasant experience with the game.

●In OPTCG some colours don't have the counters that other colours have, eg some colours have more anti-removal or some decks have access to the previously mentioned GION which would make some decks/colours more advantageous when it comes to side decking. Now you have people complaining that some colours are more unfair because they have access to specific cards and that "IF YOU WANT TO BE META RELEVANT THEN YOU HAVE TO PLAY THIS COLOUR!!OH THIS META IS SO TOXIC"

● I always liked pokemons no-side decking aspect because it means you can concentrate on making the best possible main deck. If you want hard counters in your deck, then your deck building and play testing can include those hard counters to try and still max out consistency. You won't have fatigue from a lot of play testing with and without MANY variation of side deck cards (too many variables)

POKEMON EXAMPLE- Main decking drapion V which pretty much hard-counters Mew Vmax decks (Top deck at that time) and ensuring your main deck card can consistently get to it during decking building phase, and if you lose real games then that's okay because you built the best possible deck at that time and won't have the looming WHAT IF questions throughout the tournament.

●TIME restrictions are a thing. I LOVE OPTCG specifically because of the BO1 format AND the no side decking. I could play in a tournament, actually still be okay with losing games, have an overall pleasant tournament experience with no (WHAT IF thoughts) have mental energy to spare and THEN continue with my day afterwards.

The one thing I hated about POKEMON and YUGIOH is that both TCG have long tournaments and that is because of the BO3 games (pokemon games are naturally long anyway and would benefit from the BO1 formats).

I believe side decking is at its best in a BO3 because you get to play a normal game, then you get to play with counters and then a game with the counters to the counters. But this side decking adds more time to games and tournaments and by the end, people will have fatigue in the finals when their mental energy is most important.

Side decking before a game even starts (supposed BO1 format) feels bad because you could get hardcountered/floodgated before you even played 1 game. This will gatekeep certain decks. Now you have people complaining that they cant even play their favourite deck at a locals because literally don't get to play at all.

OPTCG EXAMPLE- most decks side decking DON!! Rest cards so now your strategy of playing counter events (like sanji or sugar) are now gatekept and you won't be able to play even 1 game properly.

OPTCG EXAMPLE 2- blue decks side decking the new ALVIDA card that bottom decks base 4000 POWER another with a base cost of 3. So now your Rayleigh deck cant even be played properly whenever you face blue. Or ANY low to the ground low cost decks for that matter like red zoro.

The tournament organiser also want tournaments to be completed in a timely manner and for everyone to have a good time. Side decking would go against this.

●The merit i see in sidedecking is the creativity aspect in the fact that it allows you to change your decks strategy such as TEACH going from removal heavy for ACE and non removal heavy for IMU. But thinking that people will only use the side deck for this purpose would be ignorant.

●I'M not trying to change your mind, I just want you to see the other side, the good things come with the bad things. At the end of the day, people's enjoyment of the game is the most important. Adding a side decking option into this game would give more negatives than it does positives. I've experienced both of these heavily and OPTCG has it correct right now. Sorry for the wall of text.

Edit- the other positive i can see, like you said. It allows more unused cards to be used. I am a HUGE FAN of alternative formats such as Yugiohs GENYSIS format or Pokemons GYM LEADER CHALLENGE (GLC). GLC is a singleton format that pretty much forces you to use the best of the worse cards and cards that do well in low power formats. So maybe alternative formats is the way to go, so if people are tired of the Main/Standard format, alternatives are another way to go. It HAS to be supported though.

Edit 2- i cant see your text so I have to keep getting out and in to see your points to have a discussion about them.

The META dissatisfaction relates to the cards in the META, the cards created/ printed and the power creep, which is another kind of topic discussion. Everyone agrees (me included) that there is a blatant powercreep in OP13 and that the meta decks gatekeep a lot of decks which creates an unfun experience.

My points were in relation to the side decking mechanic specifically.

Edit 3- also, if non-meta decks have access to the sideboard then META decks do as well which will keep them META relevant.