I can't recall any MMOs that have been genuinely ruined by RMT activity.

Your original complaint, the botting activity by itself, is nothing more than a trivial annoyance. They don't effect you directly in any way and thus cannot possibly "ruin the game".

Their indirect effect on the economy is arguably noticeable, but will never "ruin the game" for various reasons including:
  • The majority of the currency these teleport botting miners/botanists gather is made through player to player sales which does not introduce additional gil in to circulation. In fact it reduces the total gil in circulation thanks to market board tax.
  • The lack of super-high end and rare (sellable) items, and the fact that this isn't IRL means everything is mostly relative. It's nonsensical complaining that the price of Item X has gone up when everything else you can farm/gather/create/sell in order to afford that item is also more valuable.
  • The Special Task Force [Unit], as evident by their performance in XI and recently in XIV, will be constantly removing gil from circulation and crippling RMT for brief periods between their ban waves.
  • Gil is for the most part worthless anyway right now.