As a Roblox developer, it is currently impossible to prevent bots from joining your game.
If Roblox is able to address this issue, it would improve my game and my development experience because I wouldn’t have to worry about bots joining the game and potentially confusing normal players. This would also prevent people from mass botting games that are on the front page.
In my opinion, and probably a few others too, I think only the developer of the game should be able to add “bot” players as some people use these bots in a misleading or mischievous way.
I believe you thought you came up with a way of malicious ‘bot users’ not being able to join your game. However though, these bots do not use some obscure Roblox API to join games. Roblox currently has no API at all to let you do this. These bots are joining games the same way as any other regular Roblox user, so in short: this would change nothing.
If dozens of experienced engineers can’t figure out an answer to the botting problem within a short timespan, it is unlikely that anything we suggest here on this forum is going to change that. It’s somewhat pointless to make these superficial suggestions for that reason. If it were that easy to distinguish a bot from a real player and prevent them from joining games, they would have already solved botting problems by now.