I mean of all the courses in any rotation Augusta is the easiest. Yes, conditions are a factor. The Open Championship is 100% determined by whether the wind is blowing. When it does it is maybe the best test, if calm conditions it is much easier.
Amen corner is such a misnomer. 13 is easy, 11 is usually an easy 9 iron in, 12, just play for a par.
And one thing why the Open Championship is so superior to the others is that they play the courses as they always have whereas even Augusta has made huge changes in the last 15-20 years to increase the difficulty factor. The U.S. open courses are just extreme where the USGA won't water the greens for 2 weeks whereas they will water the rough incessantly and won't cut it.
Well, I think I showed above how it's not in any way the easiest - it has easy years, it has tough years. Amen corner is 10, 11 and 12 and does not include 13 which is obviously easy. 10, 11 and 12 all play 1/4 shot above par for the pros. That is in no way easy. There is no such thing as an easy 9 that if 3 yards off and you're looking at bogey.
I have no problem if you think the Open Championship is the best - I love the Open. There is something wonderful about playing a course that hasn't changed (much) in over 100 years. But one could also make the argument that it's not exactly fair to be penalized two shots for putting a ball dead down the middle and catching a random 4 yard wide pot bunker.
Each of the majors has specific challenges. The Masters requires awesome iron play, great putting and ability to read greens and be creative. The US Open requires accurate drives and severely penalizes wayward shots with deep dense rough. The PGA is usually on demanding courses but doesn't have the harsh penalty for a lack of accuracy. The Open obviously favors links play (whatever that means, exactly) and usually rewards players who can handle playing in cold windy conditions. They are all great in their own right.
It's just way over the top to call Augusta irrelevant. It is pretty much the most important tournament for American players and if they can only win one of the majors, they'll take the green jacket most of the time.