It's not that you can't learn rigor and critical thinking skills as an English major, it's that it's not all that hard to complete an English degree without learning those things. Hence the word "signals".
Does this mean that grading in the humanities is more difficult or more arbitrary?
At one point during the pursuit of my BA in History, I was reading about 1000 pages of primary and secondary source material per week.
Reading primary source material is comparable to reading mathematical exposition in that you have to proceed slowly and carefully.
Then, I had to analyze the material using the various methods of historical analysis/criticism. You are not going to get an 'A' if you just regurgitate facts. You're also not going to get an 'A' if the analysis/argument is sloppy.
Math didn't really get that hard until the proof-based courses, and math degrees usually require only two of those (though I did four). The “computation courses” just consisted of exercises that are only difficult until you discover a small set of tricks.
Now, I'm not sure about what it takes to be a very successful English major, but my anecdotal evidence indicates that the high achievers are pretty smart: One did a math double major, one went from being a LaTex whiz to handling most of the IT at a mathematics journal, and the other is a better-than-average DBA.
The corporate world is deeply negative and anti-humanistic and will typecast you to the lowest calibre of person consistent with your resume. The issue in English is that the floor is lower. It has little to do with the ceiling. (Yes, there are plenty of English teachers from whom it's harder to get an A than it is to get an A in an advanced math class.) It's about what is concluded about someone when the worst possibility is assumed.
To some degree, but I definitely recall some dramatic differences in difficulty from various professors or classes that purportedly covered similar material and met the same requirements. When someone gets all A's, I always wonder whether they were one of the students who said "Why are you taking the second compiler course? That's hard. XYZ is a much easier A..." Of course, someone who doesn't have all A's could still be someone who tried that and failed, which would be kind of the worst case...
How do you know this?
(You know, since we're talking about logical rigor.)
The people who I know who didn't just complete english degrees, but excelled were all very critical thinkers. The classes required reading, understanding, and then writing critically about what was read. Thinking was highly valued, particularly about nuances of the language and meaning.
Of course people who are not good can slide by and get through school, but that can happen in any field. See CS grads who cannot write FizzBuzz for example.
I have a degree in English, and another one in mechanical engineering.
The 9 English classes that I took were uniformly less difficult and less rigorous than the 25 or so engineering classes I took. When I studied English, I already had a reasonably well-developed understanding of logic, but it was not used in my English classes. I would estimate that I could have earned a B average in English with 5-10x less time spent than in engineering. Standardized tests suggest that I have more aptitude for engineering (or at least math), so English should have been harder for me if the curricula were of the same difficulty.