It's fine as is. If you play the game as it's designed to be played, with multiple characters, stamina/energy is a complete non-issue in these games. They just need to add more character types, and more slots. Other versions have six character slots, and six characters, they could certainly stand to add more characters than that though.
Also stamina/energy systems have NOTHING to do with Korean laws, meant to limit how long people play, other the other nonsense people claim it's there to do. All those things would require something that measures the amount of time a person has been playing, but these systems instead measure the amount of content a person has consumed, if you don't measure something, you can't regulate it. Then the first, and maybe only South Korean law relating to game play was enacted just shy of six years after the first game using a system like this was released there. Finally even in those grind focused games, they have plenty of limits on rewarding content with things like daily dungeons, and daily quests, so don't try to pretend no other game uses such limits, especially since those games also limit your rewards, which is why you need to grind your life away in them.
If you want to play one char all day, this isn't the type of game for you, play something else. If they were to increase the amount of energy, or even remove it, you can bet the amount of grind would increase, as that's the balance online games on a whole work with, if it's rewarding, you can't do it too often, if you can do it as much as you want, the rewards are low. Play the games that provide what you're looking for, rather than selfishly insist established games be fundamentally altered to cater to you, at the detriment of others.