Here is the problem - parser rarely causes harassment when the player is top dps. The probability of getting harassad increases the same way player's performance decreases - healers and tanks have to live with this since start of the game. The more we delay parser the higher harassment wave it will cause.

Look at Bismark HM, people are starting to get really edgy when dps check fails. It gets cleared, but not without wipes and there are many failed runs. But everybody can clear it if they wait long enough for groups of better geared/skilled players.

Now imagine what would happen if the game's dps checks continued to increase? More fail groups. The gear is overboosted, maybe due to skill of player base, what is going to happen if developers stop putting so many stats between item levels? More wipes, increased frustration, increased need for parser. Right now game is so easy that in good enough group even toddler could reach Alex Savage.