Forewarning: this article contains some sarcasm and cynicism about a genre that is very popular and that I have enjoyed. It also has opinions which are my own and not necessarily yours. The beauty of it is that we can exchange our opinions in the comments section.
When I wrote about roguelikes, I stated that games shouldn't be denied the opportunity to relate to a certain genre based on specific genre definitions by discussing what the roguelike genre was really about and how 'roguelites' fit the bill. Now I want to discuss the other end of the spectrum with DotA clones and how people will throw any name on them that they can find, leading to frustration and confusion. DotA called itself ARTS. League of Legends called it a MOBA. Transformers Universe is calling theirs a MOTA. People try to call them 'lane-pushers' or 'hero brawlers'. Others try to bring up its vague tower defense elements. It's time for some destructive criticism.
Action-RTS is the most misleading name here. The name is probably derived from the similar naming scheme found in RPG and Action-RPG. RPG stands for Role-Playing Game, where the player of the game literally played a role in the world, creating someone with a personality, problems, goals, and a distinct set of skills. Early computer RPGs tried to keep all of these factors intact through extensive stories, dialogue with party members and other characters in the world, and having multiple solutions to every problem to allow different playstyles to be functional. Action RPGs don't bother with the role-playing aspect and choose to focus on stats, leveling, killing, and looting. All of those things were in a traditional RPG but were not the focus of the game.
This what an Action-RPG looks like. Very similar to DotA and LoL.
On the other hand, RTS stands for Real-Time Strategy, a genre defined by base building, resource management, and commanding armies. Being an Action-RTS implies that the game is a Real Time Strategy game that puts more focus on commanding armies than the other two aspects. Some games, like the classic Age of Empires II, allow the players to set the rules of the game to accomodate more action oriented play, such as fast building and high resources. Others, like World in Conflict and its predecessor Ground Control, eliminate resource gathering and base building entirely to allow the players to focus on micromanaging their armies.
But DotA has no base building, resource management, and no armies to command. There are minions, but you have no control over them. Therefore, it can't be an RTS or even Action-RTS. There are defensive turrets called towers, but you don't place or manage them in any way, so it isn't tower defense. Controlling one hero, earning gold, and buying better gear are things that Action-RPGs do. There are also monsters in the wild that can be hunted and giant boss monsters to be slain, so should DotA be called a Competitive Action-RPG?
If Action-RTS is the most misleading name, then MOBA gets the award for having the most vague name. MOBA is an acronym for Multiplayer Online Battle Arena, which describes most video games made in the last 30 years. If your game allows for two or more players, then it is multiplayer. MOBA specifies that that multiplayer must be online, which is the de facto form of multiplayer for every game on the PC, where most MOBAs are released. 'Battle' involves physical or violent conflict, which tends to happen more often than personal or emotional conflict in video games. Even the first video games involved battles of some description, such as the Cathode Ray Tube Amusement Device shown in 1947, which was "a missile simulator inspired by radar displays from World War II."
Action-RTS is what happens when you remove base building and resource management from traditional RTS.
Finally, the 'Arena' is just the location that the battle takes place in. Since every video game happens in a limited space, every game has an 'arena', especially online multiplayer battle games. These arenas are often called 'maps' and are often sold in packs after the release of the game except, ironically, in MOBAs, where the one map is so 'balanced' and 'pure' that making any changes or additions would be to the detriment of the game.
Having proved that most video games can be considered Mulitplayer Online Battle Arenas, using the term MOBA to describe a game genre as specific, intricate, and demanding as a game like DotA or League of Legends is misleading and ineffective.
Other names have come up over the years that seem to be aware of how inappropiate the most popular names are. 'Lane-Pusher' is a term that only people that play the game will understand, which doesn't help people who are new to the genre understand what the game is about. If you need an experienced player to explain what the genre name means, then you have a problem. Hero Brawler is almost a good name, except that 'Brawler' is already used to describe side-scrolling action games like Double Dragon, TMNT: Turtles in Time, and Streets of Rage, and adding "Hero" to the name does nothing to distinguish the complex, team-based, competitive game with RTS/RPG roots from the simple side-scrolling beat 'em up.
This isn't a hero brawler because there are no heroes here.
Transformers Universe decided it wanted to be a Dota clone rather than an MMORPG, and developer Jagex decided to call it a 'Massively Online Tactical Action' game . MOTA breaks the mold of bad names partly because there is nothing massive about 5v5 games. Having a potentially persistent "global faction war" doesn't compare to having literally thousands of players in the same world at the same time, like actual MMOs do. It also could be a terrible play on words by trying to sound like the word 'motor'. But mostly, MOTA is a bad name mostly because it's a Spanish slang for marijuana.
Where does that leave the name of the Dota genre? Unfortunately, I think MOBA is going to stick as the primary name for the genre due in part to the worldwide popularity of League of Legends. I would like to see the name change to Competitive Action RPG or something that highlights the true competitive nature of the game, but that isn't likely to happen.