Indeed, being paired against low level opponents is the worst thing that can happen to a top player. They basically have to win. If they win they get next to no "rating". If they lose however, they'll lose a TON.
When I was low level when I started, I wasn't a whole lot worse than I am now. I was just new. And while I was "new" to dominion (isotropic), I brought with me almost 20 years of card game experience. I was certainly not a greenhorn.
So when I was level 2, I was probably really playing at a level 20-30 range. Anyone that I beat on my way up would have lost a ton of rating, because I was a "low level player", even though I really wasn't. In most games, this is called being a "smurf" (although that more-relates to creating a new account for the sole purposes of beating up on new players, not really the situation I was in).
Regardless though, I hate playing low level players. Especially when that level 1 player opens Ambassador/Ambassador. I know he's not a true level 1. I basically must beat him, but he is a very solid player. I'm in a lose-lose situation, really.