I agree it is a dominant starting card, but I don't mind it. I think the beauty of the game is trying to overcome the luck element and that some variance is important to the game. There's only a 6% chance that your opponent is dealt Giant Dam. And then if they are dealt it, I'd say only a 75% chance they can build it in round 1 (proper defense against Giant Dam being dealt to the opponent is an important round 1 drafting strategy). So we are talking about around 4% of games where you are up against it. And, then, the opponent still probably only has an 80% chance (by your estimation) of winning? That's down to 3% of games? And that assumes that the other player is an expert (I think 500+ ELO player is accurate definition of expert in this case) and knows how to press the advantage of round 1 Giant Dam? That seems pretty reasonable to me. And I greatly enjoy the challenge of trying to overcome my opponents being dealt Giant Dam. It is a challenge, but it is doable.
I also don't consider it that much more powerful than Magnetic Train. And I think the actual most powerful thing in the game is a round 3 or round 4 Atlantis. That probably swings more games than a round 1 Giant Dam. If your opponent is going black/blue generals and you're in the lead, significantly, and going white/yellow financiers and then they spike a round 4 Atlantis, that to me is more powerful.
There are going to be dominant cards that swing games and some randomness. Overcoming that and planning for it and defending against it is the beauty of the game to me. And what makes 2-player non-expansion It's A Wonderful World, my favorite game ever by a lot, is that it is a "luck" game with a lot of randomness, but talented players can almost always overcome that luck, especially against non-elite opponents.