I'm not sure about how the things are in DotA 1's competitive scene, but in DotA 2, Antimage is all the riot. And who could even argue? Perhaps one of the hardest carry in the game, he was the most banned and first picked hero of The International with an impressive winrate of 70%. What's interesting is that Antimage's presence in games are so disliked that players casually throw around the words, "am picker" to those who actually pick him. Throughout my on and off involvement with DotA, I only recall two heroes I considered to reach the state of "broken", of which were Bristleback and Necrolyte. In all fairness, Necrolyte's strength was largely attributed to the combat regen of Heart & Bloodstone, but Bristleback was seriously GG tier at the time all by himself (he got nerfed how many times? lol). And yet, I do not recall anyone being called a "bb picker" or "necro picker". So this is pretty funny to me.
Anyhow, the matter of Antimage's strength is still debated among many DotA enthusiasts. I have my own views about this hero as well:
I suppose he was always been a strong hero by design. The challenge was always about making him actually work. This was especially hard in the old days without the Quelling Blade or Poor Man's Shield (I suppose his late game is a matter of discussion as well before the Manta change). Not forget to mention that the general players' understanding of the game weren't as strong as they are now. And now, all of those limitations are gone.
Actually, more than gone, some new elements of the game had been introduced that makes Antimage even more effective. For one, the corpses do not block the neutral spawns. This allows Antimage to blink from camp to camp farming endlessly. Secondly, in DotA 2, the ancient dragons can be cleaved, and more creeps have mana (whereas in DotA 1, only 3 neut creeps had mana). All of these add quite a bit of equity in Antimage's farm rate. And with these changes, it's no surprise that he's finally risen to the top of the tier list as one of the strongest heroes in the game.
So then, how do we stop him?
What's clear about Antimage is that he needs time to grow. He doesn't have much of an early game or mid game, but only his ridiculous fast-paced late game which hits by 25-30min. However, this is if you let him get there. Time is most certainly of the element.
Quick story: I once played a game in DotA 2 where I had finished a game by 23 minute mark. That is twenty-three minutes. I'm sure you all understand how fast 23 minutes is in a game of DotA. It is obscenely fast. And we throned it too. Yes, it was a stomp. But it's not like I've not stomped before, and I've never throned by 23 minutes before. The sick thing about this was that Leshrec was the only real pusher on the team, and the opponents fought back until the end. Frankly, I don't even think games ended this fast when push strat was popular. What's interesting is that these 20-25 minute games happen casually in DotA 2.
Now, imagine a game where a team is designed to push, and that you can end the game before 20 minutes. Most Antimage can get their battlefury by around 15 minute mark if he has a good game. And even if he does get it by 15min, how is he going to find any room to grow when his base is getting hammered all throughout the game?
If indeed a team can end a game pre-20min, I agree with the statement of my good friend Chuck: "That would really be an opening of a new age."