I'm sorry, but nothing in what you're saying is telling me "instaroads are a problem". All you seem to be saying is how Arcane monolith works, and believe me, I know... are you complaining that Arcane Monoliths are too OP? Because I think that argument has been done to death (see my post earlier about sneak attacks).
Yes they are a problem, unless you tell me to see appears magically a road traversing uncharted areas full of monsters just because you signed a deal with an AI is not a problem. It just blew the interest in the game for me. I like to explore and stress for my bold adventurers. If they can use a x4 road to explore, I say meeeh... the 'no one ever went here, what lies beyond' spirit is totally destroyed.
Another example, last turn in an Altar game 2 AIs apparently secured a deal that created a road that traversed all my little kingdom at once, linking 3 of my cities in a row, and I had yet to discover the tech that create roads between cities (I was focusing on magic). Totally a let down, sorry.