I actually agree with this to a certain extent.

It's certainly not applicable to the argument when it comes to Heroic raiding, and with LFR, I would say that we now have a means of making encounters to an "entry level" without making normal mode "entry level" as well.

However, since I feel that raids have been, should be and must be a continuous learning curve, I would like to see a change to what defines a good, bad, average and awful tank.

For me, it should be as follows;
Awful tank - Doesn't pay much attention to what's going on. Often dies due to poor CD usage and unable to maintain threat because all they do is autoattack.
Bad tank - Mostly has timing issues. Slow to react, but at least they're trying. Don't understand the encounter enough.
Average tank - Good at keeping themselves alive, easing the job of "their" healers, utilises raid mechanics well enough to get some advantage
Good tank - Expert at CD timing, pays special attention to their co-tank, uses raid mitigation at the best moments, looks ahead of the raid's mechanics to maximise progress on a boss

Something like that. That way, learning to tank in normal isn't a wipefest, being average doesn't get you benched and being awesome simply means you spend less time on an encounter once it has been mastered.