Unfortunately, this is not a true statement. I raid and I care about my DPS; however, as I play on PS4 I do not have access to a parser without becoming a burden upon someone who has. I don't like wasting other people's time and asking them to sit there and feed me numbers seems like a waste that could easily be avoided if I was given the tools to do it myself.
By all means, let's completely ignore the legitimate uses a parser has. It is first and foremost a tool to determine DPS output and places of improvement when tight DPS checks need to be passed. To claim it has no value beyond e-peen is an absolutely ridiculous statement if you have ever done Savage content in this game.
While you are absolutely right that it is just a number, they are the only numbers which we cannot readily measure. Standing in avoidable damage is easily identifiable. Failed mechanics lead to heavy damage or wipes and are, thus, easily identifiable. Handling adds in proper manner commensurate with your role is again easily identifiable. etc. etc. I can readily observe and determine all of these things as I work through a fight and improve to perform all of these tasks. Without pouring over the battle log with a calculator for 30 minutes, I cannot tell you the % efficiency which I performed my rotation while meeting the other metrics. With DPS checks and enrage timers, this is absolutely a metric of successfully clearing a fight. It cannot be argued that efficiency in performing rotations for ALL party members has 0 bearings on clearing.
DPS checks are their own mechanics. If I move during the full stop mechanic of A10S, I have visual feedback of an attack hitting me as well as my health immediately dropping and possibly death to inform me that I failed that mechanic. If I constantly wipe my group to DPS checks by underperforming, it is much much more difficult to determine that I am the cause with absolutely 0 feedback other than the whole group wipes. As I've seen this argument play out so often, I presume that the response will be "it's everyone's job to perform the DPS check, if you're underperforming then it's up to the group to make up the slack" which is true; however, that's a carry and is likely worse than a failed DPS check as it gives me positive reinforcement that my DPS was good enough when in actuality my DPS wasn't good enough but several of my teammates were overperforming... as I move forward, I will eventually hit more and more walls of DPS whom are not capable of covering up my errors. However, since I have that previous reinforcement that I CAN meet DPS checks, I am less likely to identify myself as the cause of my own inability to progress. This can just as easily lead to people lashing out at their party members as a parser can.