Are there any decisions at all for the player in a "flat bet" game? Or is it simply a game of 100% chance then, with all skill/reading your opponent removed?
There is a basic strategy to learn that is "optimal" about when to take each action, but it is easily memorized, and I wouldn't call it much of a skill element. Now, if you track cards, you can claw back a little bit of the advantage by varying the strategy dependent on what cards remain, but going very deep on this is a lot of work for not a lot of payoff.
You get a much bigger payoff by simply betting big when the deck is in a favorable shape, and continuing to follow roughly basic strategy.
Fixed betting as described is exactly the same as varying your bets, in both cases you're playing roughly basic strategy with varied bets, it's just that in fixed betting your vary your bets by having the big better change tables rather than by having an individual change bet sizes, because this is harder to detect.
For the people with a flat bet (on a card counting team) there’s no decision making at all. They simply follow basic strategy which prescribes exactly what move to make in each situation.
It is/was also possible for a player at the first seat of the table to see a sloppy dealer's hole card when checking for blackjack. This is called "first basing" while using a teammate is generally called spooking.
So they are working hard keeping that count, but they are not directly playing as if they know anything. The roaming fake rich guy is.