Here's the documentary (it's kind of more of a commercial but it's still pretty good if you're interested in esports)
1. In some roles and metas, the split second mechanical difference does matter i.e. for carries or mid-lane playmakers under specific metas and specific matchups. Although some metas are less mechanically deep for certain roles -- I know part of the theory for Dendi's decline is that his mechanical skill was overkill when denies in midlane (very timing based mechanic) became less important compared to macrostrategy (meaning that he couldn't just 'out skill' opponents and win the game with an early lead).
2. But, the experience gains from being in competitions for a long time make the older players a great fit for coaching, captain, and support roles.
3. But another factor is less reaction time and more that the late 20s and early 30s players have spouses and more expansive lives beyond the game, so they simply cannot spend the 100+ hours a week perfectly tuning the midlane or hard carry meta where the fundamentals can change really fast. Also, for the most successful players (read: millionaires) they want to enjoy their wealth and do things outside the game.
I think this is the biggest factor in the same way most devs don't stay in the same job for 20 years (particularly the top ones!).
Additionally, most games change a lot over their lifespan; what made someone a top player in the early days doesn't necessarily continue to benefit them now, and mindset/skillset changes are not easy to make. Poker is a great example of that: pros from 20 years ago might have experience, but if they're not up-to-date with the cutting edge of theory and solvers, their 'experience' will get them crushed.
Otherwise, yeah, you can be Divine/Immortal using game knowledge and have terrible reaction times relative to the greater player base.
I'm immortal ranked Dota player, that spends 10 hours a week playing Dota. And has played DOTA since Warcraft 3. My reaction time is slow, because I think so much about each situations. And a slightly bad decision can lose the whole game. When I see my team fighting, I take a short look, maybe think for as long as 2-3 seconds and make a decision about if I can contribute to the fight or if I will just be feeding.
DOTA is a lot more about strategy, positioning, how to pressure, farming patterns, vision/warding, when to use power spikes and be a team player. This is also why experienced players beat the crap out of younger players and probably also why younger players play something else than DOTA/MOBA.
> And a slightly bad decision can lose the whole game.
A slightly bad reaction time can lose an entire game. When you're looking at pro games - where real money is on the line - you want the player who has the same decision making ability as other highly ranked players but ALSO the ability to react really quickly. Failed to disjoint a projectile in time? International lost. Didn't pop your BKB in time? International lost. Didn't hex a puck or ember fast enough? International lost.
Like, sure, again... you can go really far in dota with poor reaction speed. I'm 30, for example. But when it comes down to creating a five man team to compete for money then very few teams are going to pick up older players on the chance that they might not react fast enough. Old man fear was called old man fear for a reason.
Also, this makes me really curious about what the age composition is for immortal top 100s for each region. How many are there over the age of 30?
The WaPo article seems to imply that is not true.
Also, in Formula 1 reflexes, hand-eye coordination, reaction time, etc. are all extremely important.
Despite that, a driver will typically be at their peak in their early-mid 30s.
On other hand there is lot of value with experience and some patience, if you are mid-line team a experienced driver who can support the team and bring the car back in whole or even with some points race after race is not horrible investment.
The only "game" I can think of which is close is war.