It is selfish when it is your dps causing people not to clear, ive seen people reach the 3rd or 4th fight of a raid tier who can do mechinics perfectly but are atrocious at dealing damage. End of the day dealing dps is a mechanic itself when it comes to harder content, and it is selfish not wanting to improve it for the betterment of your party. Having the ability to see who is underperforming would prevent entire groups having to dispand instead of just the one whos holding people back