Basically, I am saying that having something extra to guess is inherently more competitive, not less. This is one of the reasons the addition of abilities and items was good
This is true up to a point, but once you start adding in too many things to think about it becomes more and more of a guessing game rather than skill.
For the last few generations, Pokemon has been relatively balanced in terms of how many options you have per turn. Every turn, you can choose one of 4 moves, or make a switch to one of 5 Pokemon. Therefore, every turn you have to pick 1 option out of 9
, based on which of the 9 options you expect your opponent to pick. Often, there will be 4ish options that are objectively quite bad ("choking"), 3 that are pretty good if your opponent makes the corresponding move, and 2 that are generally safe and "good". Each turn you have to work out which of those 9 options is the best for you to take. There will be situations where 2 options are almost indisinguishable, particularly in the late-game and therefore causing coin flip situations, but for the most part there's tons of skill in a 9-option metagame. [Note: In gens 6 and 7 there are slight deviations to this, because 1 Pokemon per team can Z-move or Mega which means that on one turn per game there's 10 options]. If I have 9 options, and you have 9 options, then every turn can go one of 81 ways.
Dynamax in Gen 8 OU flips this on its head, because it effectively adds an extra 4 options to consider every single turn up until Dynamax is activated. Every turn we now have 13 options per turn
each meaning 169 outcomes.
This would be handleable if the Max moves just did damage, cos you'd still probably only have a 2-3 objectively good choices per turn. But all the Max moves all have secondary effects, meaning that in some way or another they are basically all good options on any given turn. Without Dynamax, Close Combat into a resist is a bad option, but with Dynamax, Max Knuckle into a resist is legitimately good. So rather than having 2 good options out of 9 per turn, an attacking Pokemon now has 4-6 really good options per turn factoring in dynamax (e.g. If you have Barraskewda out vs a water-weak Pokemon and Toxapex is in the back, you can 1) Liquidation to try and KO, 2) Psychic Fangs to predict 3) switch to something with a better Toxapex match-up, which are all pretty good options. But Dynamax adds in Max Geyser if you want to set-up Rain, Max Knuckle for attack boost even if Pex comes in etc etc). Its much more difficult to then pick between those 4-6, especially factoring in that your opponent can also Dynamax. Its for this reason that people say that Dynamaxing is unpredictable - ultimately in turns into guesswork because offensive Pokemon commonly have multiple options that are equally good and almost the same risk:reward, and there's little skill in picking between them AND that's even if you know which Pokemon is actually going to do it. The number of times I've seen legimitately very
good players lose a game because of 50:50s regarding whether the opponent will Dynamax or not is absurd.
This also has particularly shitty ramifications for Choice items, which are obviously very very good but are limited by the fact that after attacking, you now only have 6 options per turn (1 attack + 5 switches). But Dynamax opens up all those options for you again, meaning that even somebody making objectively the best plays against something like Darm has to play a complete guessing game because the limitation on their item now just doesn't exist. With specific relevance to Darmanitan, Dyanamaxing at the right time and Max Quaking a Toxapex can be an auto-win, but this is a 50:50 basically every turn because there are so few switch-ins to CB Icicle Crash already.
tl;dr Up to 9 options per turn has tons of skill, but if you add in an extra 4 super powerful attacks every turn that boosts stats then its more of a guessing game. Too many good options per turn with dynamax involved that predicting when it'll happen is just a myth. Obviously you can still be skilled this generation but I'd argue the skill cap is way lower and there's tons more guesswork, may more situations where "if he does x I win, if he does y I lose".