Take for example these 2 missions.
For a 24 cool-down per tank, these missions are more suited for a game mode with no cool-down. This Event is far too silver intensive, from the consumables which cost credits, to the expensive Stimulant.
Let's say you encounter and kill 5 hedgehogs per game, each has 170 HP, resulting in 850 Damage to those types, but more realistically you would only get 0-3. For scenario 1, you finish the mission in 13 games, for scenario 2, with 3 hedge hog kills per game, that's 22 games. This is impossible to achieve without any credit spending, and difficult to achieve without spending obscene amounts of credits.
Source: https://www.reddit.com/r/WorldofTanks/comments/ji4p9z/minrys_grind_problem/
