Sure, you can easily whiff and hit lands or spells that aren't useful (Counterspell, Comet Storm, etc.) but generally speaking this ability is going to be well worth using
It is a huge mana sink, but with infinite mana or a large amount of it, you mostly guarantee a loss of life enough to kill the table after they run out of permanents
Dinosaur decks typically focus on winning through combat, so youll have plenty of chances to draw cards whenever your dinos deal combat damage to a player
The easiest battles to flip, Invasion of Gobakhan and Invasion of Zendikar, each enter play with three defense counters
Your removal and draw suites let you outlast both, with Terror in particular lacking a deep enough threat pool to really oppose you
That's likely due to Tolkien's high-fantasy world being so similar that one could imagine Middle-earth as just another of Magic's many planes