The long answer: That really depends on what kind of datapack you are talking about. Some datapacks (the much simpler ones) only modify loot tables, or add simple advancements, or add recipes and those datapacks are totally fine for use on servers where performance is a concern. In fact, I'd argue that datapacks do those simple things better than a plugin could. BUT, some datapacks make use of functions which basically just run a group of commands, and they do that every tick, for as long as they are loaded. This can result in thousands of commands be run every second changing or reading the state of the world, and that can have a serious effect on performance. This plugin uses the Bukkit API's event system to dramatically reduce the cost on server performance.