There is actually plenty of strategy, especially in BTD Battles 2. You have to manage your money well and choose the right towers, and build correctly to have a strong defense, especially if you want to not lose any lives.
Battles 2 adds the extra element of sending bloons at your opponent to get more money and put pressure on your opponent, and In Monkey City, the Contested Territory (a multiplayer endless mode), you get less money when it hits the harder, pretty much MOAB only stages