Thank you for your feedback and ideas !
About the most mentioned user not being the user people are looking for, that's why @checky first checks its suggestions against steemians previously mentioned by the author and then, if it doesn't find any match, it defaults to suggesting the most mentioned on the blockchain. It will also soon check against the followers/following of the author before the most mentioned to refine even more its suggestions.
I don't really understand your first suggestion so I won't comment on it yet. Your second suggestion though is a really good idea ! I will start working on a !more or !suggestions command to see all of @checky's suggestions for a supposedly wrong mention.
While I see where you are coming from with the bot needing to be case insensitive, it just wasn't worth it, especially with HF20 and the RC cost of comments being pretty high. Most of the mentions (about 80%) it gave suggestions for were not Steem usernames even though there are lots of checks in the code to avoid usernames from other platforms as much as possible. I will however soon add a command to the bot to let users decide whether or not they want @checky to be case insensitive when checking their posts, this should help steemians that like to capitalize Steem usernames.