4-5 civs on average, maybe 8 in worst case ? That is very, very far from going random.
Furthermore, pros have 10x more time to play than the average player and thus are expected to master more civs. For normal players it’s unreasonable to ask them to play all 35, they will necessarily have more experience with certain civs and win/lose will depend largely on whether they rolled a civ they are familiar with.