Hello
I play a lot Res Arcana, I'm now in the top 30, sometimes "only" in top 50... I don't choose my opponent, it's open to everyone.
And most of my opponents are beginner ! So you could think I'm playing the strategy you describe, but it's not a choice ! I accept every challenger, and I'm proud of it : when a was a beginner, I was extremly happy when I had the chance to play against a strong player !
And when I win against a beginner, I win 0 ELO. I've just won against a player with 150 ELO, and I paid attention to the points I won in order to post it there : I won 1 ELO point... If I had lost (and it's very possible to lose against a 150 ELO !) I think I had lost about... 20 pts ?
So the strategy you describe doesn't seem very efficient...