There are a lot of competitive titles that have reached this point in competition. Beating out a specialist of any game is tough. If you play multiple titles, and you are competing against someone who only plays a single game that is.
However, it's all about patience, practice, and determination. Beating the arcade score is definitely still in reach as it is, surprisingly (at least I'm surprised). The MAME score is also reachable, but the dedication to the game has to be there. All records are beatable, and there may still be things to discover, as with any video game.
I don't think the Kong titles are necessarily the hardest records to beat, but they certainly are up there. The other thing is that many arcade world records (and world records in general) are a lot about luck. Not to say there's no skill involved, but just that luck IS required to top many world records due to the randomness of a game, etc.
This is why in some ways I like deterministic games with patterns. In this case, it is all about your ability to optimize the game rather than avoid its nonsense. Both are enjoyable, but I prefer that my mistakes kill me rather than the game itself killing me.
All records are beatable. If you really want to beat a record, you will...unless you give up.