Yes, universities tend to excel and be superior to other universities in particular fields (with UNSW being a well-regarded university for engineering as you mentioned), and this may be accurately indicated in field-specific ranking.
QS and
Times Higher Education are generally considered quite reliable in terms of their approach to ranking universities. Both provide overall as well as field-specific rankings, allowing you to compare universities as a whole, but also gain insight relevant to your particular study interests by comparing universities in terms of specific fields.
With that being said, it is important to note that such rankings are largely informed by each university's level of research output. This means that the amount of research that a particular university conducts and publishes contributes significantly to its position relative to other universities. This is an area where Go8 universities tend to excel, given the fact that they are research-focused institutions.
It is also important to keep in mind that a university being better than another university in a particular field does not necessarily mean that the other university is bad in that field. Both universities may offer good programs. As a university student, other important factors that you need to emphasise are your academic performance as well as work experience that you can gain during your time at university. Here, you may find that a particular university is a better option for you because it may offer a work experience component (such as an internship), which can increase your employability as a graduate.
I hope this helps!