Nothing is stopping someone from making controllers that will automatically press forward at the right times. There are plenty of programs out there that can use timers for key presses or look up data inside of a text file (for turn speed or even the heading). Its just that the AI already has everything coded.
When we use AI vs AI, it doesn't matter how precise things are because both bots have the same capabilities (you could always make a smarter AI).
When we do human vs AI, its only fair that the AI has some advantages over the human player (since we generally have an advantage when it comes to flanking, targeting specific components, or waiting for the right times to attack).
The issue here is not that Melty Brain is unrealistic (as the topic name suggests) but that it is unfair/unbalanced (as Sage has repeatedly pointed out). Then again, the same could be said about a majority of RA2's more optimized designs (flails, popups, crawlers, etc.). Melty Brain just happens to strengthen an already powerful AI type. Though if this was the issue, you could just as easily make a smarter AI for some other AI type.