So is writing.
When I was a young teenager, my eyes still aglow with enough hormones to drop a rampaging buffalo, (and more to the point, still thought that such a state was, in fact, the normal one of existence) I wanted to be a writer. The very last thing in the universe I wanted to be was an artist, because I knew that being an artist meant you were poor and/or flaky. Therefore I wanted to be a writer. (The flaw in this logic should be obvious, but I was young.) And so I wrote. I wrote Very Bad Novels and Very Bad starts to stories and poetry that transcended the merely bad and went into realms that can only be expressed in scientific notation.
And during this time, I decided that writing was harder than art, because a book can take years to write, and I have to hold the reader's attention for days at a time. Whereas a painting takes perhaps a week, and if I can keep the reader amused for a minute, I've succeeded wildly.
A few years later, I went into art. And I was forced to readjust this analysis, because while the bit about attention span is still true, there is a great deal of sheer technical skill to art that has no real equivalency in writing. Everybody learns grammar in grade school, or should, god willing. But it takes years to master the raw technical skill of drawing, to be able to even render something, let alone make something interesting out of that rendering.
Virtually anyone can be a bad writer, but it takes significant effort to become even a bad artist.
At the same time, I think it's easier to critique art than writing, because an awkward paragraph or a fundamentally crappy story is hard to nail down. But with art, at least with realism, you just look at a painting, figure out the internal logic (anatomy, lighting, perspective, etc) and then tick off where the painting fails to meet its own internal logic. There's often something WRONG that you can get your teeth in--i.e. one eye is higher than the other--rather than the highly subjective "I don't believe this, and I don't like the character." Of course, on the other hand, there's also grammatical error that you can correct in writing, and once you get past the basics in art, you're left with pretty nebulous categories--"My eye goes off the page here and never comes back on" or "I keep getting drawn to this spot, and there's nothing there."
You could work quite a long time on a very bad book. I know I spent months, nay, years, on unreadable tripe. A painting, however, tends to be make-or-break in three days, and after that, it's either good to go or gone.
So now I don't know. Possibly you always think that whatever you're good at is hard to do, but easy to critique, because that's your thing. I still write, occasionally, but since art is what I care about and sweat over, of course I'll think it's hard.
Of course, it would be easiest to say "art and writing are equally valid and just as tough as each other and artists and writers work just as hard and it's all bloody subjective anyway," but sheesh, where's the fun in leaving it at that?
Addendum: It just occurred to me that there's another area where writing is definitely easier, and that's presentation. If I tell you "A beautiful woman stood in the moonlight with a chicken in her hand," you believe me. There she is. No question. Woman, check, beauty check, moonlight, check, chicken, check. That took us about ten seconds. You believe in that woman.
If I paint a beautiful woman in the moonlight with a chicken, it takes three days and at the end, you say "She's not very beautiful, your lighting is coming from the wrong direction and flattens out, and that's a duck."
Of course, this goes the other way, too...