Seeing the amount of details taken into account, any increase in player count is impacting more than you seem to think
If I theorize much, taking an example :
On ETQW, Sewer map, during a comp match, the GDF attackers got with 3 rocket soldiers and 1 Spec Ops (a rather unusual setup for an engineer oriented objective at this point of the map) in an Armadillo vehicle, rushed to a wall protecting the ennemy base, tricked-jumped on top of the wall, the Spec disabled an incoming Cyclop, and both RL soldiers killed it without the cyclop being able to retaliate
They probably had rehearsed it for long, they new exactly what path the Armadillo had to take to be the fastest possible at the wall, without being noticed by other Stroggs, they knew the trickjumps to perform, the Spec knew when to throw its jammer, the soldiers knew the positions from where to shoot without harm from the Cyclop
More to the point, they knew the Cyclop would be alone because it was 6vs6 format, and the Strogg had to counter a possible full engineer rush at first objective (which had already been proven to be efficient) with their 5 other players, and needed the Cyclop reinforcement because the Cyclop was THAT important. Ie : the Cyclop was sure to come, and would come alone, so they could do their tactic.
It was the opening move of one of 4King match, if I’m not mistaken. It worked to perfection.
With all these parameters to take into account, any additional player is going to add a lot of randomness in the possible opposition you’ll encounter. In above case, it could mess up the strat because the Cyclop could be with another Strogg who could kill Soldiers. Could… could… could… the strat is now more about something that “could happen”. It becomes random, you “hope” the Cyclop is going to be alone
If I theorize less :
In a 10vs10 or 8vs8 scenario, match will be a mess, and more about “how to react to random event” than “how to plan properly”
Reacting to more randomness is indeed more challenging in a way, but I’m not sure it’s for the better