Firstly, while some firms may also have strengths in the same practice ares as SPB has, it is unlikely that there will be many firms having strengths in the same exact suite of practice areas like SPB. For instance, Quinn Emmanuel,
Slaughter and May, and Debevoise all have strong contentious practices, but do not also have equally strong employment practices. Thus, your strategy could consist of listing several practices areas for which (when taken in conjunction) SPB is the best firm. Now, it is unlikely that good employment and contentious practices will suffice, as there are likely to be some other firms that also have that. Nonetheless, the more practice areas you add, the more other firms will you be able to exclude. Thus, by the point at which your answer is 'SPB's has a unique position in the market becasue of its strengths in employment law, contentious work + X practice area + Y practice area', I would not expect many other firms to fit that exact description. Thus, your answer will not sound generic.
Secondly, another way to approach this is to dig deeper in a firm's expertise besides its Chambers ranking. You can research and find in what particular segments of a practice area SPB is particularly good at. Some of the questions you might find it useful to consider are:
- Are there any types of cases or other mandates that the firm advises on more often than others? Are they in any particular sector of the economy?
- Has the firm had a particularly long history in the practice area, which gives it a superior reputation?
- Has the firm advised on any particularly important matters?
- Can the main client base of the firm's practice be distinguished from that of other firms? Does SPB target a particular segment of the market?
- Are there any awards/other recognition from the legal press showcasing the quality of its practice or top practitioners? Has the firm recently hired any top practitioners in the field?
- Has the headcount or revenue generated by a given practice area significantly increased?
Among others, I think you might find the Legal 500 rankings as particularly useful when researching sector expertise instead of just practice area expertise.
Thirdly, you can look beyond pure practice area/sector expertise. Essentially, the question asked in the SPB application could be interpreted as 'What are positive features of our firm from a client's perspective when they compare us to other firm?s'. From a client's perspective, a strength can consist of a feature of a firm which is not that closely related to expertise. Essentially, you should look at the firm on the whole, and from the perspective of a client rather than an applicant ask yourself what might attract you to it. For instance, a firm might be a market leader in legal tech, which maybe can automate many of the tasks that other firms staff their trainees/associates on. This can save a client lots of money and can therefore be highly attractive.
Finally, remember that this question is not a 'Why the firm' question and therefore you do not need to individuate your answer to a level of specificity that no other law firm would qualify for. It simply asks you to pace SPB in the context of its competitors in the market . As such, the firm will not expect you to find further specificity where there simply isn't from a client's perspective. As such, if you have narrowed it down to a point where the strengths you mention only apply to a very few other number of firms, you do not necessarily have to go a lot deeper.