Double the number of bots in COOP. Make half of them camp around the map in random places around and on the way to objectives and stay put.
This will address two issues:
1.) People want 'slower' action with careful room clearing instead of just running across the much larger map to the next objective. This would solve it completely.
2.) Bots currently for the most part just walk out in the open and slowly navigate to objectives/players. It usually makes them easy prey for the players, it makes engagements usually quick (followed by running straight to objective @point#1). This is not a very authentic nor engaging experience.
Doubling the number of bots and making half of them camp in various locations would solve these problems and make COOP far more enjoyable, building on the foundation that makes the mode and this game stand out and be loved by all of us.
An issue may arise from this:
Players will just not encounter all of the camping bots if they stick together and follow one path rather than spreading out and going alone across all map. I believe that this is a very good thing and that's why I think that the number of bots should be doubled and the camping half should stay put. If players follow basic tactics and practice teamwork by staying together, they'll benefit by not only being able to support and cover one another, but also having fewer enemies to fight on the way to the objective.
Another issue is, what to do with the camping bots once the players advance? They can't just run back through the players. There's a simple enough solution to this: If the players are defending the current objective, make them attack that objective from behind. If the players are not defending that objective, just teleport the camping bots to new camping locations on the way to and around the next objective.