Only problem is where do you draw the line... If a player makes a half break or is tackled in the last line by the fullback, then should a desperation legs tackle be considered dominant?
IMO it shouldnt, the attacking team needs to be rewarded for their good play and getting 1-on-1 matchups. Best way of rewarding the team is a quick play the ball, and a back pedalling defence.
The only way it should be applied is if a defender makes a legs tackle in the front line, and chops the ball carrier down with a text book tackle. They are getting punished here because their tackle is so effective it doesn't give time for a 2nd or 3rd player to get in an slow the play-the-ball down (would be penalised for a flop), hence the ball carrier gets a fast play the ball despite an ineffective run.
In saying this though, it would create more grey areas in the game. Should just stick with how it is, and try and eliminate wrestling and gang tackling. Speeding up the game is what needs to be done, not slowing down the fast, exciting aspects and hoping this will solve the slow wresting parts.