Let's look at this from a logical perspective.

If you and one other person apply for a job at the same time, whomever is hiring will check what you are capable off before making a decision. If you can only meet the bare minimum requirement to perform the job and the other person can not only perform the job, but also do many other tasks and do them more efficiently. Who do you think will be deemed superior and hired?

Df works a bit differently seeing as you cannot choose who the healer is(unless premade or you yourself are a healer). So instead of hiring a better one, you have to make due with the one you've been given. Doesn't mean you wouldn't have preferred a better healer that makes the most out of their kit.

Now this thread has mainly been about healers, but I judge other dps players and tanks the same I would judge a healer. Most people I know judge bad play in general, it's just healers sitting around doing nothing is more obvious. Hence why I promote public parsers.

TLDR;
All players should aim to perform to the best of their abillity and be held accountable.