I can't not admire Icefrog dedication to Dota, the game is very complex and yet its very balanced and diverse.
Now, before you say this hero is never picked or viable, let me give you some perspective.
Once upon a time, BKB (the item which gives magic immunity) had 10 seconds duration and 80 seconds cooldown, with no diminishing returns like the modern version.
This means any magic based support would turn useless as soon as the enemy get BKBs. This also shows why a hero like Enigma used to be so popular since he had an AoE disable which goes thru BKB. You had a kingdom of haves and have-nots and that's why people picked agility carries so much in the past, because they were not countered by BKBs so heavily.
Now look the modern days… BKBs duration goes down with every use so your carries aren't invencible superheroes forever, there are also dozens of abilities now which simply go thru BKBs meaning you can't cover all your bases with a single item.
My point is, on the days of Dota 1, when people said «this hero is not viable» it mean it. If you picked Crystal Maiden for example you either finished the game in 20 minutes or you had one less hero in the game. All her abilities were countered by an item and they had 10 seconds to kill her and move to the next target.
Of course, some heroes are favored and I'd risk to say some heroes are simply better given their versatility and overall power at all stages of the game, however, I believe most heroes now are viable and scale well into late game, which is a feat given the 100+ number of heroes Dota have.
Good job Mr. Lizard.