This is just blatantly false.

It is false. They don't need them by any means. In some specific cases, bots do help, but this is usually a result of poor design. An example would be any expendable resource that is required in large amounts, but is very boring and unrewarding to gather. In these instances, bots can be argued to be a positive. But for bots to exist to farm these boring resources, they must also exist to farm end-game content. If they exist at all, the negatives will always out weigh the positives. The positives exist, sure. But they're few and far between.

From a regular player's perspective, if they want to kill a boss for 3 hours, they must use X amount of Y resource. If the cost of Y resource is very high, or worse, the market has not enough supply, the game becomes less fun for them.

This is addressed by bots, but is better addressed by a design solution from the developer.

All of that being said, if bots exist, the reward for going and farming that boss is going to be far less than if bots didn't exist. So still, negative.