In my opinion, english is not easy at all for selective schools test, mainly because of time constrictions and ability to work under pressure. There is no extra time to read and think (doing those is crucial for english) therefore making it hard
Also, for primary school students who don't bother to learn english properly (as in expose them to a wide variety of things that are "english") it would make it much harder for them to do well in english
If we are arguing on the basis of time constraints and performance under pressure, then other parts of test are far more difficult.
In english you are expected to complete 45 questions in 40 minutes. For most questions, you won't even have to read the entire text as the questions are designed to target specific lines or words. As long as you can find these phrases in the text, the questions are one-dimensional and simple enough holistic understanding of the text is not needed.
For GA, there's 60 questions in 40 minutes and the questions in this section sometimes require actual thinking. You are required to be able to very quickly identify patterns and solve a wide array of problems from different areas. Your timing will be easily thrown off here if you have not seen the types of questions in the section before.
Maths has the greatest discrepancy from what is in the test to what taught at a primary school level. There are questions here involving constructing your own algebraic equations from written problems and what are essentially some basic sequences and series questions. You need to have strong time management here and be smart in your methods to solve problems.
As for writing, this section is actually insanely difficult to pick up marks at the high end and not worth your time in terms of it's contribution to your overall score. For a year 6 student to be composing a creative writing piece in
20 MINUTES, they need a lot of practice. If you had not prepared for this section, you would be easily blown out. I remember in my first attempt at this section I only wrote 1/2-3/4 of a page. By the time I sat the test, I was comfortably writing 2 pages. Your ideas need to come so fast for this section that there's no real time for planning - anyone not used to the timing here would get destroyed. If I had known what rote learning was back then, I probably would've rote learned a piece.
In comparison to other sections in the test, reading comprehension is actually quite straightforward. If you went into the test without any prior prep, it would make the least difference in your reading comprehension.