ESS is definitely easier content- wise. It's the kind of subject many people take light heartedly because you're right; similar to how Math Studies is for those who don't have an aptitude toward math, ESS is for non- science oriented students. It's kind of basic, really- just environmental stuff, not too simple, not too complicated, with LOTS of case studies involved.
However, the thing with this subject is that a lot of people are too complacent about it- the world average for it is surprisingly low. Also, the mark schemes are picky; they have specific words and terms they want you to use in your answers, and it doesn't always seem fair when you nail the explanation/ theory behind something but just used one word instead of the technically correct term and get 2 marks off. Also, because it's not considered very challenging, many people do reasonably well in the exams and the grade boundaries get set very high. Statistically you're more likely to get a 7 in Bio SL than ESS, but practically, you'd have to work harder for a 7 in Bio- in ESS it would be a matter of luck as well.
In my school, the subject was underestimated miserably, to the point where our ESS class didn't even have a proper teacher- half the time she wasn't there and when she was, she just told us to read the textbook, and we struggled with the labs quite a bit. So if your school doesn't neglect it, you should be fine. Our class got 4's and 5's all around, mine was one of the few 6's- but I hardly paid the subject any attention, and I'm not a science-y student at all- so you should be alright, too. Definitely take ESS if you're struggling with Bio- it'll only get easier, that's a guarantee. Universities really won't care if you're not applying for a science.