OK, without being too technical, I will try one more time to explain how bots cripple the servers with lag. Sorry if this does not make sense, but trying once more:

Amount of data stored, as long as you do not reach the size limits of the database system in use and as long as the databases were not horribly designed slows the system down, but not horribly. In a typical database, look-up times increase by a factor a maximum 5-10% each time you double the amount of data being searched through until you reach complexity limits. Evony should not be close to complexity limits so cutting half of all data out of the game would be a trivial gain on the server side. As to costs, total data saved on a server is cheap as mass storage is cheap and simply not a issue.

Bandwidth however is the great limiting factor in all computing. This is how much data you can have moving across through a limiting choke points, the routes, switches, and other parts of the network. When data throughput reaches anything over 10% of the limit of any one of the choke points data flow begins to slow down, data errors begin which requires the network to retransmit packets of data which further lags the system and creates a deteriorating situation which spirals to a lock. These bottlenecks are like hoses, you pay for the size of the hose. It can be a straw size, the level of server which could handle old 300 BAUD dial up modems, or it can be a fire hose that can handle terrabytes per second. The provider charges geometrically higher for the size of hose you need, that is if you double your bandwidth, your charges my go up by a factor of 10.

Most humans may play the game 2-3 hours a day, max. During that time, they are limited how many commands they can execute and how close together they can do those commands, but each one sends data to Evony, and gets data back. Each time another player does something to them, again, they received data. That is multiplied by the 100's of players online at any given time. Anyone offline affects the total amount of data stored, but has zero effect on bandwidth. A human cannot be actively sending commands from more than 1 city at the same time, nor from more than 1 account and it takes them real time to switch between. With a bot however, that player can have 100's of accounts active at once, and thousands of cities. They will be active 23 hours per day. So the amount of data that one "player" is sending through that pipe every day has not be doubled, it has gone up by factors of 1000's. And there are players out there running several hundred alts, that is single players using more server bandwidth than an entire server of human players would use.

Anytime there is a hick-up of the network you can see the affect of this. If you refresh an account in the middle of the day you can quickly get logged back in, even though that is a lot of data that transfers when logging in to update the status of your game. But when there is a server bounce, even after the server comes back up, it may take you an hour to get logged by in. This is not because anything is still wrong with the server, it is because a few thousand bots are out there trying to all log back in at once and bringing the login bottleneck to its knees choking it with requests and data.

A common battle tactic is when you are attacking someone you know is defending with a bot to send a huge number of attacks at them, both the account you are attacking and other accounts you know they are running on the same computer. This overwhelms their bot, chokes it, and it dies. It does this by choking that computers memory and communication bandwidth, not their storage memory, the bot dies, their city gets destroyed. That is what is happening continuously with the server.

Yes, the severs have always had lag. When the game first began, the data required to be transfer to the players was beyond what the servers could handle. Servers and network bandwidth have improved vastly since then. The data required per command and to run the game in general have only increased marginally. The number of people actually playing has probably gone down. But the number of accounts and cities per server has gone up vastly and lag is beyond choking and it is because of bots, not the number of players.